CLEANING LIQUIDS FOR MOTION PICTURE FILM
This article was published by the Society of Motion Picture Engineers in August 1927. The authors were from the Research Laboratory, Eastman Kodak Company. It should be noted that most of the solvents mentioned in this article have either been banned under the Montreal Convention because of their ozone-depleting properties or have been banned for health reasons. Carbon Tetrachloride is thought to have caused liver damage and also can be converted into phosgene if drawn through a cigarette.
Transactions of S.M.P.E., August 1927
CLEANING LIQUIDS FOR MOTION PICTURE FILM
J. I. Crabtree and H. C. Carlton[ 1]
It is necessary to clean motion picture film at various stages in its progress from the laboratory to the theatre to remove:
1. Dirt on the base side of negative or positive film;
2. Dirt or grease which may accumulate on negative film during printing;
3. Dirt and oil which accumulates on positive film during projection.
1. When processing in the laboratory by the reel and tank system, if all excess water is not removed from the film previous to drying, any dissolved salts present in the water supply remain on the film after evaporation of the water. The residual salts are usually only visible on the base side of the film because on the emulsion side they have an opportunity to diffuse within the gelatin coating during drying.
It is necessary to clean the back of the dried film either by wiping with a damp chamois while on the drying reels or by passing the film through a cleaning machine. Such treatment is unnecessary in the case of positive film if all excess water is removed previous to placing on the drying reel by thorough wiping or squeegeeing.
In the case of negative film it is customary to wind it with the emulsion side downward onto a wooden drum covered with cloth when the base side may be cleaned without danger of injuring the image. The cloth should be removed from the drum at frequent intervals for cleaning.
A suitable cleaning liquid for the above purpose should possess the following properties:
(a) It should be capable of dissolving traces of inorganic salts and should also dissolve or emulsify grease and mineral oil;
(b) It should be sufficiently volatile and should not cause the gelatin side of the film to swell in a period of several seconds if it accidentally has access to it;
(c) The liquid should not affect the physical properties of film with safety or nitrate base or remove the color from film with tinted base.
A suitable mixture fulfilling the above conditions is the following:
Metric Avoir.
Ammonia (conc.) 5 cc. 2/3 oz.
Water 95 cc. 12 oz.
Denatured alcohol (see below) to make 1000 cc. 1 gallon
The ammonia serves to emulsify any traces of grease or oil, while the mixture contains sufficient alcohol to prevent dangerous swelling of the gelatin if any of the mixture reaches the emulsion side of the film.
A choice of several alcohols for preparing the above liquid is available as follows:
Grain alcohol (ethyl alcohol). This is the most satisfactory for the purpose since it has a minimum effect on the film base.
Denatured alcohol. Ethyl alcohol is available containing a variety of denaturants. The most common denaturant is wood alcohol which dissolves nitrate film base so that this should be avoided if possible.
The most commonly available denatured alcohol is motor alcohol. The “Pyro” brand of the Industrial Alcohol Company is prepared according to the following formula No. 5 of the U S. Internal Revenue Bureau:
Ethyl alcohol 100 volumes
Wood alcohol 2 volumes
Pyridin bases 0.25 volumes
Kerosene 0.5 volumes
On diluting this with water the alcohol turns milky owing to the kerosene coming out of solution. Kerosene has no effect on the film base or gelatin coating and serves to dissolve grease. Although pyridin and wood alcohol attack the film base when pure, in the above concentration and when diluted with water in the above formula they have no harmful effect on the film base during the time required for cleaning. The above cleaning liquid prepared with “Pyro” motor alcohol had only a slight tendency to produce curl on film with nitrate or acetate base after complete immersion for 24 hours at 70°F.
Isopropyl alcohol. This is now available commercially and the “practical” grade is satisfactory for the purpose. It does not turn milky on mixing with water and has little or no curling effect on film with either nitrate or acetate base even on immersion for several hours. It is non-poisonous[2], is not decomposed on exposure to light and when used in the above mixture does not attack the silver image or the gelatin coating.
Tertiary butyl alcohol is also available commercially and has properties similar to those of isopropyl alcohol. Its odor, however, is somewhat objectionable.
All the above alcohols tend to remove more or less of the tint from nitrate or safety tinted base film but the water present in the above cleaning liquid greatly retards this action.
The precise effect of cleaners prepared with the various alcohols on the tinted base is shown in the following table. Samples of film were immersed in the cleaners and the times required for visible signs of removal of the color were observed.
Effect of Film Cleaning Liquids on Tinted Base Film
Formula Safety Base Nitrate Base
Ammonia (cone.) 5 cc. Liquid slightly Same as safety base
Water 95 cc. colored in 10
Motor alcohol to 1000 cc. minutes
Ammonia (conc.) 5 cc. No effect in 2 Liquid slightly
Water 95 cc. hours colored in 10minutes
Isopropyl alcohol to1000 cc
Ammonia (conc.) 5 cc. Slight effect in No effect in 16 hours
Water 95 cc. 1 hour
Tertiary butyl alcohol to1000 cc.
The propensity of the cleaner to remove the tint varied with different colored bases but the above table gives data for the base which was most readily attacked. Since the period of application of the cleaning liquid is very much shorter than that required to visibly affect the tinted base, the cleaners are considered satisfactory.
2. When making positive prints from negative film, the negative accumulates more or less dirt, grease, and loose particles of dust which must be removed at frequent intervals. In any case it is advisable to remove dust after every third or fourth passage through the printer by passing through silk plush (cut on the bias) moistened with a suitable cleaning liquid as the film is being wound on a re winder. More thorough cleaning of the emulsion side can be effected by winding the film base side downward on a cloth-covered drum as above.
The requirements of a suitable cleaning liquid for this purpose are similar to those for positive film dealt with below.
3. Positive film accumulates more or less dirt and oil during its passage through the projector which causes spots and patchiness on the screen. In this connection film which has been toned has a greater tendency to show oil spots than untoned film, which is presumably a result of the matte surface produced by certain toning processes. The oil and dirt may be effectively removed from the film by immersing in a suitable oil solvent, with or without scrubbing, and then removing the excess solvent by squeegeeing and buffing. . satisfactory machine for this purpose has been described by Faulkner.[3] A less satisfactory method of applying the solvent is by means of silk plush as the film is being wound on a rewinder.
Various liquids have been suggested for the above purpose but the precise effect of such liquids on the film base and on the image, as far as is known to the authors, has not been investigated. More over, in certain cases deterioration of the film image has been definitely traced to the use of unsuitable chemicals. An investigation to determine the most suitable liquids for the above purpose therefore seemed desirable.
Requirements of a Suitable Film Cleaning Liquid
A suitable film cleaning liquid should possess the following properties:
1. It should readily dissolve fats and mineral oils;
2. It should not affect the gelatin coating or the film base, or remove the color from film with tinted base. Also it should not attack the silver image or a tinted or toned image even on prolonged contact in the presence of moisture, because when cleaning on a rewinder any excess of solvent which does not evaporate is trapped between the convolutions of the film, when it can evaporate only very slowly;
It should also not decompose on exposure to light to give products which are injurious to the film;
3. The boiling point and latent heat of vaporization should be such as to permit of sufficiently rapid drying;
4. It should be non-combustible, non-toxic, and be readily available at a reasonable price.
At the outset a survey was made of all the possible commercially available non-inflammable and inflammable oil solvents, and the most promising of these were investigated as follows.
Non-Inflammable Oil Solvents
The following compounds were selected by virtue of their suitable volatility, solvent action, and price:
Solvent Formula Boiling Point
Dichlorethylene C2 H2Cl2 56-60ºC
Trichlorethylene C2 HCl3 85-87ºC
Tetrachlorethylene C2 Cl4 119-121ºC
Ethylene dichloride C2 H4Cl2 83ºC
Carbon tetrachloride C2 Cl4 76ºC
The effect of these compounds on the film was investigated as follows:
Effect of Non-Inflammable Solvents on Motion Picture Film
The effect of the above solvents on film was studied by placing a strip of developed positive motion picture film (nitrate base) in a 100 cc. stoppered bottle with 40 cc. of the solvent and 3 cc. of water at room temperature. The film was thereby subjected both to the liquid and its vapors. Any tendency of the film to curl or of the image to change color was observed after 18 hours with the following results:
Condition of Film (nitrate base)
Solvent after 18 hours at 70°F.
Dichlorethylene (pure E.K.Co.) Slight curl when wet. Bad curl when dry. No effect on image.
Trichlorethylene (Com.E.K.Co.) No effect on film base. Emulsion softened and image obliterated.
Trichlorethylene (pure E.K.Co.) No effect on image or film base.
Tetrachlorethylene (Dow) Slight curl when dry. No effect on image.
Ethylene dichloride (pure E.K. Co.) Bad curl. No effect on image.
Carbon tetrachloride (Dow) No effect on base or emulsion. Carbon tetrachloride (pure EK.) No effect on base or emulsion.
Any curling tendency in the above tests was an indication that the film base had been attacked. The tests show that dichlorethylene and ethylene dichloride exert a solvent action on the base, while commercial trichlorethylene affects the gelatin coating and the image; these liquids are therefore unsuitable. Further tests were made with pure trichlorethylene, tetrachlorethylene, and carbon tetrachloride at 95°F. as follows:
Effect of Non-Inflammable Solvents on Motion Picture Film at 95°F.
Solvent Condition of Film (nitrate base)
Trichlorethylene (Roessler & Hasslacher) No effect on base. Image turned slightly brown in four days.
Tetrachlorethylene (Dow) Image attacked at surface of liquid
at end of four days.
Carbon tetrachloride (Dow) Started to curl at end of six days.
No effect on image.
Carbon tetrachloride (pure E.K. Co.) Started to curl at end of eight
days. No effect on image.
Carbon tetrachloride (taken from fire extinguisher) Film curled at once and turned
brown above liquid at end of
three days
.
Any effect of the above solvents on the image was attributed to decomposition in the presence of water with the liberation of hydrochloric acid. A sample of old tetrachlorethylene which was strongly acid was treated with anhydrous sodium carbonate which would remove any acid present, and this sample had no effect on the image. Another acid sample was treated with anhydrous calcium chloride to remove water but this affected the image showing that hydrogen chloride when dissolved in the solvent and in the absence of water will attack the image. To confirm this, dry hydrogen chloride was passed into pure dry carbon tetrachloride The resulting liquid attacked the silver image bleaching it to white silver chloride.
The above tests indicated that of the solvents tested, carbon tetrachloride is the most resistant to decomposition by heat and moisture.
Effect of Light on Solvents.
Since on storage, solvents are subjected to the action of light, the effect of exposure to light on the rate of decomposition was studied. In order to secure an accelerated effect, the solvents were exposed in open bottles in the presence of moisture to a quartz mercury vapor lamp for from 5 to 30 hours. Strips of film were then immersed in the light exposed solvents for varying times and any effect on the base or silver image was observed.
The acidity of the samples was also determined by adding an equal volume of water, shaking thoroughly, and titrating with dilute normal caustic soda. As shown by the following table, the effect on the film image was roughly proportional to the quantity of hydrochloric acid present
Effect of Light on Solvents at 70°F.
Time of
Exposure to Acidity
Mercury (cc. N/1O
Vapor Lamp NaOH) Remarks
Trichlorethylene None 0.12cc. Slight curl. No effect on image in 10 days
(Roessler & Hasslacher)
Trichlorethylene (R.& H.) 5 hours 1.10 cc. Film badly curled.
Image bleached
in 2 days.
Tetrachlorethylene (R.&H.) None 0.12 cc. No effect on film in
10 days.
Tetrachlorethylene (R.&H.) 5 hours 0.65 cc. Image destroyed in
2 days.
Carbon tetrachloride. (R.&H.) None 0.09 cc. No effect in 10 days.
Carbon tetrachloride (R.&H.) 31 hours 0.09 cc. Image turned brown
in 10 days.
The above results show that trichlorethylene and tetrachlorethylene under the influence of violet light and moisture undergo decomposition. The compounds are probably oxidized to phosgene (COCl2) which is decomposed by moisture to form hydrochloric acid and carbon dioxide as represented by the following equations.
C2Cl2 + O2 = 2COCl2
Tetrachlorethylene oxygen phosgene
COCl2 + H2O = 2HCl + CO2
phosgene water hydrochloric acid carbon dioxide
The hydrochloric acid formed attacks the gelatin causing it to soften, and likewise converts the image to silver chloride. The extreme toxicity attributed to old or impure samples of compounds of this type is undoubtedly due to the presence of phosgene.
Of the non-inflammable compounds tested, carbon tetrachloride most nearly approaches the ideal film cleaning liquid as outlined under the above list of requirements. It is especially valuable since when pure it does not readily decompose under the influence of light to form compounds which are injurious to the film. However, in order to prevent any possible deco on storage, it should be kept in brown bottles or opaque containers.
Inflammable Film Cleaning Liquids.
In addition to non-inflammable solvents, a survey of possible inflammable liquids was also made because it was considered that in the event that an otherwise suitable liquid in this classification was discovered, its objectionable inflammability might be partly overcome by admixture with carbon tetrachloride.
The only promising solvents under this classification were benzene, toluene, xylene, gasoline and allied petroleum distillation products. Tests with these compounds, similar to those made with the non-inflammable compounds above, showed that none of the solvents affected the silver image, but benzene and toluene caused film with nitrate and acetate base to curl after immersion for 2 days at 70°F. All these solvents evaporate more slowly than carbon tetrachloride which in some cases may be desirable.
It was considered that possibly these compounds might be considerably less toxic than carbon tetrachloride, in which case it would be desirable to use them with the addition of only sufficient of the tetrachloride to remove danger of explosion.
Toxicity of Benzene, Gasoline, and Carbon Tetrachloride.
Although no practical toxicity tests were made with the solvents under investigation, adequate information is to be found in the literature. Tests with animals have shown that benzene, gasoline, and halogen substitution products of the hydrocarbons such as carbon tetrachloride all produce varying stages of poisoning resulting in dizziness and unconsciousness, and finally death.
Lehnann[4] found that with cats, air containing 20 to 30 mg. per liter of benzene causes loss of consciousness in a few hours and 42 mg. per liter produced death. Hamilton[5] quotes a large number of cases of benzene poisoning in industry, some of which resulted in death.
Haggard[6] experimented with dogs and found that the toxicity of gasoline was about one-half that of benzene.
Lehmann,[7] working with rabbits, found that 240 mg per liter of carbon tetrachloride were necessary to produce death in two hours. Although no data were found giving a direct comparison between the toxicity of carbon tetrachloride, benzene, and gasoline, a survey of the experiments of Haggard and Lehmann indicates that carbon tetrachloride is less toxic than benzene and slightly more toxic than gasoline though this depends on its purity. Few cases of industrial poisoning by carbon tetrachloride have been recorded and these deaths were probably due to the use of an impure product which may have contained an excess of phosgene and hydrogen chloride. Since the presence of 3 to 5 mg. per liter of carbon tetrachloride imparts a strong odor to the air, there is no excuse in practice for the concentration approaching the danger point, which is 10 times this concentration.
The Suitability of Carbon Tetrachloride for Cleaning Motion Picture Film.
The above experiments indicate that carbon tetrachloride when pure is quite satisfactory for cleaning motion picture film. It is a good solvent for oils and fats, evaporates readily, is non-combustible, and is readily available at a reasonable price. It does not affect the image even on prolonged contact and has a minimum tendency to decompose on exposure to light in the presence of moisture. Although toxic when impure, the pure compound is no more toxic than benzene and if reasonable ventilation is provided, it may be used with relative safety.
Tests also showed that carbon tetrachloride has no curling effect on film with nitrate or safety base after two days and it does not remove the color from either nitrate or safety film with tinted base.
Manufacturers such as the Dow Chemical Co. and the Eastman Kodak Company supply sulphur-free carbon tetrachloride which is satisfactory for cleaning film. A few years ago many commercial samples of tetrachloride contained sulphur chloride which was formed as a by-product in its manufacture by the action of chlorine on carbon disulphide. On exposure to the air in the presence of moisture sulphur chloride deposits sulphur which is capable of combining with the silver image to form yellow silver sulphide. Such samples of carbon tetrachloride containing sulphur chloride when left in contact with motion picture film attacked the image, especially in the presence of moisture, and bleached it out to a faint yellowish-white image of silver sulphide No such commercially impure samples of carbon tetrachloride have been encountered within the past two years.
Mixtures of Carbon Tetrachloride with Inflammable Solvents.
In some laboratories and exchanges a mixture of carbon tetrachloride with high test gasoline is used for film cleaning. This mixture evaporates less readily than pure tetrachloride which may be an advantage in some cases. Its adoption in the past was a result of the toxicity of impure samples of tetrachloride, a 50% mixture by volume with gasoline reducing this considerably. This mixture burns with great difficulty and is satisfactory from a fire hazard standpoint although the proportion of the two liquids necessary to give a non- inflammable mixture depends on the nature of the gasoline. It is considered that pure carbon tetrachloride is to be preferred to such a mixture for general purposes.
Film Moistening Liquids.
In addition to accumulating oil during projection, both the film base and gelatin coating lose moisture and tend to become brittle owing to the excessive heat to which the film is subjected. If the film were allowed to cool to room temperature between successive projections, little trouble would be encountered, but in practice the film does not cool off sufficiently between successive projections and the resulting baking process drives out the moisture, which results in brittleness.
If film which has been rendered brittle in this manner is exposed to a moist atmosphere even for only a relatively short time it tends to regain its flexibility. It is not possible to do this by placing the tightly wound reels of film in a humidor or a vessel containing water because the moisture penetrates the convolutions of film very slowly. It would be possible to humidify the film satisfactorily by passing it continuously through a humid chamber or by winding the film in contact with a damp strip of paper or other absorbent ribbon. Such a system however, is inconvenient in the theatre or exchange.
A satisfactory method of moistening film is to immerse it in a mixture of water and a water-miscible volatile liquid such as grain alcohol. The percentage of water to be used in the mixture depends on the degree of brittleness of the film and the time which elapses between application and evaporation of the liquid. If an application machine of the Dworsky type is used, this depends on the rate of passage of the film through the machine. During this short period little or no swelling of the gelatin coating occurs, but sufficient moisture is absorbed to restore the flexibility of the dried out gelatin coating. Moreover, when the film is wound up in a roll, the dried out film base can also absorb moisture by virtue of being in contact with the moistened emulsion. Film base absorbs moisture relatively slowly so that little or none is absorbed by it in the period of application of the moistening liquid.
At the outset a survey was made of possible water-miscible volatile liquids which could be used for the purpose. The requirements of such a liquid are identical with those for the film base cleaning liquid already outlined, choice of the following liquids is possible; grain alcohol, denatured alcohol, isopropyl alcohol, and tertiary butyl alcohol.
The exact quantity of water to be added to the alcohol must be determined by trial. From 15 to 25 per cent water is usually satisfactory and this proportion holds in the case of all the alcohols named above. The condition of the film after treatment will indicate any necessary changes in the proportion of water to be added. If it is too tacky less water should be used and if too dry and brittle the quantity should be increased.
A mixture of either of the above alcohols with water has little or no solvent action on mineral oil which may be present on film after projection. However, in practice the rubber squeegees in the Dworsky machine tend to emulsify and remove traces of oil. If much oil and dirt is present on the film a moistening liquid which is also capable of dissolving oil must be used.
Combined Cleaning and Moistening Liquids
It is possible to incorporate a mineral oil solvent such as carbon tetrachloride with any of the above alcohol-water mixtures. The quantity of carbon tetrachloride which can be added depends on the quantity of water present in the alcohol. For example: tertiary butyl alcohol and carbon tetrachloride, and water and tertiary butyl alcohol are miscible in all proportions. Water and tetrachloride are immiscible, but if water is gradually added to a mixture of the alcohol and carbon tetrachloride with shaking, a uniform mixture is obtained until a critical quantity of water has been added, beyond which the mixture turns milky and the liquid separates on standing into two phases or separate layers. The quantity of water which a given mixture of the alcohol and carbon tetrachloride will hold depends on the alcohol content and on the temperature, the mixture holding less water at lower temperatures.
A curve showing the limiting quantity of water which can be added to mixtures of tertiary butyl alcohol and carbon tetrachloride in varying proportions is given in Fig. 1. Commercial samples of the alcohol are apt to contain varying quantities of water. The data are for a practical grade of tertiary butyl alcohol which was practically anhydrous.
The miscibility curves for grain alcohol, denatured alcohol, isopropyl alcohol, and tertiary butyl alcohol are approximately identical for all practical purposes. For the preliminary experiments the following formula was used as a cleaner;
Of the cleaning liquids prepared according to the above formula the one containing denatured or grain alcohol had little or no solvent properties for mineral oil so that it had no advantages over a plain alcohol-water mixture.
Fig 1 Miscibility of Water-Carbon Tetrachloride-Tertiary Butyl Alcohol. Please click Image to see larger image.
When prepared with isopropyl alcohol the mixture dissolved 1 per cent of light machine oil and with tertiary butyl alcohol about 3 per cent of oil. Since the quantity of oil on dirty film is never such that the concentration of oil in the cleaning fluid would exceed this, the isopropyl and tertiary butyl mixtures were considered promising.
In order to determine the effect of the above mixtures on the film, strips of safety and nitrate motion picture film with plain and tinted bases were immersed in glass bottles containing the various liquids and stored for several days at 70°F. The results obtained were as follows:
Effect of Cleaning and Moistening Liquids on Motion Picture Film at 70°F.
Effect on Effect on Gelatin Effect on
Formula Film Base Coating and Tinted Base
Image
Water 15 cc. Acetate Changed silver image Slight solvent
CCl4 10 cc. Slight curl to white silver chloride action in 5 min.
Isopropyl Nitrate in 20 hours
alcohol Slight curl
to 100 cc in 20 hours
Water 20cc. Acetate No effect on image Acetate
CCl4 10 cc. Slight curl Slight solvent
Ter. Butyl in 20 hours action in 20 min.
Alcohol Nitrate
To 100cc. No effect in Nitrate
20 hours No effect in 60 min.
In the case of the isopropyl alcohol mixture an interaction between the alcohol or possibly an oxidation product of this and the tetrachloride occurred causing the liberation of hydrogen chloride which attacked the silver image, converting it to silver chloride. Although neither isopropyl alcohol nor carbon tetrachloride when used alone attacked the silver image, on mixing the two in the presence of water and adding a little silver nitrate solution, a white precipitate of silver chloride formed within a period of a few minutes. No such action occurred with tertiary butyl alcohol.
The interaction of the alcohols with carbon tetrachloride in the presence of water was investigated further by exposing mixtures prepared with the different alcohols to ultra-violet light. In the case of mixtures of tetrachloride and water with denatured alcohol and isopropyl alcohol, the image was attacked in S hours. No effect was obtained with a mixture containing tertiary butyl alcohol after exposure for 24 hours.
Of the combined cleaning and moistening liquids tested, the following was the most satisfactory:
Carbon Tetrachloride 10 parts by volume
Water 20 “ “ “
Tertiary butyl alcohol 100 “ “ “
This has no harmful effect on the film, it dissolves a sufficient quantity of mineral oil and it humidifies the gelatin coating. If it is necessary to increase the quantity of water in the formula, the proportion of the ingredients to give a clear solution is indicated by the miscibility curve in Fig 1.
The capacity of the unused liquid for dissolving mineral oil is limited, but with use the liquid will dissolve a greater proportion of oil as a result of dehydration of the liquid by virtue of the absorption of water by the gelatin coating of the film. Unless the liquid is used for long periods it is usually not necessary to add a further quantity of water to compensate for that absorbed by the film.
If the film to be cleaned is coated with an excess of oil the above solution may not entirely remove all the oil with one treatment and a second treatment may be necessary.
Experiments have been made with the additions of glycerine and ethylene glycol and mixtures of these to the above solution but the results indicated that these are usually not necessary.
An alternative method of moistening the film is to first remove the oil with carbon tetrachloride and then give the film a second treatment with a mixture of denatured alcohol or tertiary butyl alcohol and water in the proportions outlined above. This involves more labor but is a very satisfactory procedure.
Practical Recommendations.
1. For cleaning the base side of negative and positive film after processing the following solution is recommended:
Ammonia (conc.) 5 parts by volume
Water 95 “ “ “
Alcohol[8] to make 1000 “ “ “
The solution may be applied to positive film by means of a cleaning machine and to negative film when wound face down onto a cloth covered drum. Negative film may be cleaned with safety on certain types of sprocketless cleaning machines, but it should not be handled on machines fitted with sprockets owing to the possibility of damage to the film.
2. In order to remove dust and finger markings from negative film it should be cleaned before printing by wiping gently with silk plush moistened with carbon tetrachloride (sulphur-free) as it is being wound on a rewinder. An electric fan should be arranged so as to blow a current of air across the film in a direction away from the face of the operator. The cleaning process should be repeated after every third or fourth print has been made.
3. For cleaning film which has accumulated oil and dirt during projection, carbon tetrachloride (sulphur-free) as supplied by the Dow Chemical Co., is recommended. For cleaning brittle film the following solution at the same time removes oil and moistens the film thus tending to restore its flexibility.
Carbon tetrachloride 10 parts by volume
Water 20 “ “ “
Tertiary butyl alcohol to make 100 “ “ “
The quantity of water in this formula should be varied according to conditions. If the film is too moist after treatment less water should be used in the formula and if too brittle more water should be added. In this case it will be necessary to increase the quantity of alcohol also so as to retain the water in solution.
The cleaning liquid may be applied to the film in the same manner as outlined under (2) above. This method is not always satisfactory because if the solvent does not evaporate thoroughly before the film is rewound, more or less solvent is retained between the convolutions of the film and in case an impure solvent is used this will be liable to attack the film image on storage. A film cleaning machine of the type recommended by Faulkner is to be preferred.
In the case of very brittle film two successive applications may be necessary. The odor of tertiary butyl alcohol may also be objectionable in hot weather.
An alternative procedure is to first remove oil from the film with pure carbon tetrachloride and then moisten the film by passing through a mixture of denatured alcohol, isopropyl alcohol, or tertiary butyl alcohol with 15 to 25 per cent of water.
Although air which contains sufficient carbon tetrachloride to smell perceptibly is not dangerously toxic, ample ventilation should be supplied when using this or any other solvent. In the case of a film cleaning machine, a suitable exhaust hood with carry-off pipes should be arranged over the machine.
Carbon tetrachloride as received in drums often contains a small quantity of water in suspension as fine droplets. Unless the water is removed before use, spots will be left on film after cleaning as a result of local swelling of the gelatin by the water.
The water can be removed readily by pouring the liquid through a vertical glass tube containing granules of anhydrous calcium chloride. A tube 4 or 5 feet long, 3 or 4 inches wide, and fitted with an outlet tube about one-half inch in diameter is satisfactory. A wad of absorbent cotton at the bottom of the tube serves to retain the calcium chloride granules.
To use the column the carbon tetrachloride is poured in at the top and allowed to n out at the bottom directly into the dispensing bottle which has been dried previously. Several gallons can be passed through the apparatus in a few minutes. The calcium chloride should be thrown away and replaced occasionally. Usually several hundred gallons can be treated with the quantity described above. Both ends of the tube should be stoppered when the apparatus is not in use, otherwise the calcium chloride will absorb moisture from the atmosphere.
REFERENCES
[1] Research Laboratory, Eastman Kodak Company.
[2] H C Fuller, Chem. & Met. Eng. 29, 538, 1923.
[3] Faulkner, Trans. S. M. P. E. 25, 117, 1926.
[4] H. B. Lehmann, Arch. für Hyg. 75, 1, 1912.
[5] Haggard, J. Pharmacol & Exp. Therap. 16, 401, 1920.
[6] “Industrial Poisoning in the U. S.” by A. Hamilton (Macmillan).
[7] H. B. Lehmann, Arch. fur. Hyg. 24, 1, 1911.
[8] The “Pyro” brand of denatured alcohol of the Industrial Alcohol Company is satisfactory, although isopropyl alcohol or tertiary butyl alcohol are to be preferred.