International projectionist (Jan-Dec 1952)

and are so uncertain in strength as to be unfit for running through a projection machine. The best practical solvent for highacetyl base is a watery liquid called dioxane. Some scientists, especially in Europe, are inclined to regard dioxane as being too toxic to be slopped about in any except well-ventilated rooms. Film manufacturers, while agreeing that dioxane is mean stuff, pooh-pooh the notion that its use will harm projectionists. And the film manufacturers are probably right. Dioxane has what is called by biochemists and pharmacologists a "low-grade" toxicity. It is probably less poisonous than wood (methyl) alcohol, carbon tetrachloride, and other toxic materials projectionists occasionally work with. Since most commercial safety-film cements contain dioxane (or ought to contain dioxane if they are to work properly), breathing the vapor of it and getting some on one's fingers is unavoidable. But so far not one case of dioxane poisoning has turned up in the theatre field. Because dioxane has a rather high boiling-point (and also because it is somewhat expensive) more volatile solvents are mixed with it, reducing the dioxanecontent down to about 50%, making a cement that is more rapid in action (and also lower in cost) . These more volatile solvents may be, and ordinarily are, only partial solvents for cellulose triacetate, but in combination with dioxane they work excellently. There are also combinations (rather than mixtures) of other solvents and partial solvents that may be incorporated into good safety-film cements. High-acetyl base is quite soluble in chloroform. But for some strange reason, a splice made with pure chloroform is rather weak unless made under great pressure. Chloroform is, like dioxane, a poison; but we have never heard of anyone being poisoned by using film-cements containing it. Amyl acetate, discussed just a moment ago, is an ester of amyl alcohol and acetic acid. There are many other liquids belonging to the class of simple esters; but the only common one that exerts an appreciable solvent action upon high-acetyl base is methyl acetate. This can be used as one of the ingredients of a film cement containing dioxane or other solvents. The use of glacial acetic acid commends itself only when no regular safetyfilm, cement is available. It sets quickly to form a moderately strong flat splice with high-acetyl safety film. It should never be considered as a satisfactory substitute for the best commercial cements, however. Its action can be improved by mixing other chemicals with it. The highest cellulose acetate, the triacetate, is slowly soluble in cold glacial acetic acid, but rapidly soluble in the hot This illustration shows a mixed roll of fluorescent-treated safety film (white) and untreated nitrate film (dark) on an exchange reel. (Photographed with an ultra-violet source.) The edge of the treated safety film is actually colored purple and the nitrate film black in ultra-violet light. acid. At room temperatures the solvent action of glacial acetic acid for safety base is increased to an appreciable extent when certain other solvent liquids are mixed with it. Just as nitrate base is unaffected by either alcohol or ether alone, but is dissolved by a mixture of alcohol and ether, so high-acetyl safety base dissolves to a satisfactory degree in an acid splicing mixture such as glacial acetic acid, plus choloroform, plus acetone. However, formulae that work extremely well with high-acetyl safety film are not always to be trusted with nitrate film. Chloroform, for example, has no effect al all on nitrate base. The wearing quality of safety film seems to be a big bone of contention. A typical complaint runs somewhat like this: Durability of Safety Film "Take a look at this print. It's a fairly late release, and not a scratch on it; but the sprocket-holes are already badly cracked at the corners. It wasn't that way when we had nitrate prints. A nitrate film has to be practically run to death before perforation damage begins to show up." Other complaints even involve contradictions. For example: "Safety film is simply a manufacturer's scheme to make more money. Because it wears out more quickly than nitrate film, the distributor must order a greater number of prints of each picture. That means greater raw-stock sales." That is one fellow's opinion. Another projectionist says: "Safety film wears out before distributors can get a reasonable number of runs out of it. Instead of ordering more prints of each picture, the exchanges start bicycling prints to avoid repairing the worn-out prints themselves." The writer cannot accept paradox as paradox any more than the reader can. (Continued on page 27) Underwriters' Bulletin on Cellulose Acetate Film As a pendant to Robert A. Mitchell's discussion of nitrocellulose and cellulose acetate stock in this issue, IP here adds excerpts from National Board of Underwriters' "Special Interest Bulletin No. 283 — Film, Motion Picture Cellulose Acetate." The repeated insistence, in this Bulletin, upon the importance of continuing to observe all customary safety precautions as long as nitrate film continues to circulate is particularly important to IP's readers. FOLLOWING an extended investigation, acetate base film in the form of ribbon for motion pictures was listed by Underwriters' Laboratories Inc. as slow-burning, the fire hazard being classed as somewhat less than that of common newsprint paper in the same form and quantity. Motion picture safety film having a cellulose acetate base is now being marketed for commercial and general use. It is claimed that this film has a greater projection life and is otherwise superior as compared to the older type of cellulose acetate film. This type of film may be identified by the words "Safety Film" printed at frequent intervals along the edge. In case of doubt, acetate film may be distinguished from nitrate by a burning test, using only a small piece of film, and burning it in a room where there is no film and no fire hazard. Nitrate film will burn fiercely; acetate film will burn quietly. The ignition temperature of cellulose acetate is between 700 and 800° F., as compared to about 300° F., for cellulose nitrate. A temperature of about 500° F. is required to produce the decomposition of cellulose acetate film. In the neighborhood of this temperature the evolution of fumes in material quantity occurs. These fumes are irritating and suffocating, but not considered to be toxic under most conditions. The decomposition of cellulose acetate film once started does not continue except under conditions where there is an external source of heat. On the contrary, in the case of cellulose nitrate film the decomposition continues when once started, even in the absence of external source of heat. This difference of decomposition is, therefore, of great im(Continued on page 34) INTERNATIONAL PROJECTIONIST • November 1952