An Investigation of the Gaseous Decomposition Products of X-ray Films

Abstract

THE original purpose of this investigation2 was to determine the decomposition temperature of nitrocellulose X-ray films and the toxic gases evolved from decomposing nitrocellulose and cellulose acetate films. The analysis of the gases was limited in this work to the determination of their hydrocyanic acid content. The concentrations of the other toxic constituents, namely, carbon monoxide and the oxides of nitrogen from nitrocellulose films and carbon monoxide from cellulose acetate films, have been well established by other investigators. The base of a nitrocellulose X-ray film consists of a mixture of nitrocellulose and camphor similar to celluloid. The camphor imparts plasticity to the mixture. The base of the film is covered on both sides by a thin layer of gelatin impregnated with silver bromide. The explosiveness of nitrocellulose is in direct proportion to the degree of nitration of the cellulose. In films the nitrogen content of the nitrocellulose is about 11.7 per cent, whereas it is as high as from 12.4 to 13.5 per cent in explosives such as guncotton and smokeless powder (1). Films in which the nitrocellulose base is replaced by cellulose acetate are called “safety” films, because the cellulose acetate is stable at temperatures at which nitrocellulose decomposes. Celluloid burns only when brought in contact with a flame (2). Flameless decomposition will take place, however, if a sufficiently high temperature is attained, in which case the celluloid decomposes with the evolution of large quantities of gases. According to Worden (2), gases are given off which form explosive mixtures with air. These gases, the products of incomplete combustion, are formed in a limited supply of oxygen. They consist mostly of carbon monoxide, nitric oxide, methane, and hydrogen, and combination with oxygen takes place when they come in contact with air. Although nitrocellulose at room temperature will not decompose to the point of combustion, some deterioration takes place. Worden says that nitrogen peroxide is liberated when nitrocellulose is stored. Farmer (3) explains the decomposition of nitrocellulose as follows: “A catalytic decomposition can take place in the presence of nitric peroxide. It occurs in the absence of moisture and accelerates itself autocatalytically. It consists of an internal oxidation of the nitric ester, aided by atmospheric oxygen, which re-oxidizes nitric oxide evolved by the nitrocellulose to the nitric peroxide. This is absorbed by the nitrocellulose and causes further decomposition.” Experiments undertaken by the Chemical Warfare Service (1), in its investigation of the conditions incident to the disaster at Cleveland, show that “X-ray film, if stored in large quantity, will decompose if subjected to a temperature of 100°C. or higher. The decomposition point for periods of heating not exceeding several hours is near 135° C.