6. Preservation by Chemical Substances. — For many years it has been the custom to em ploy salt, sugar, alcohol and saltpetre for the purpose of preserving meat and fish, and some of these substances for the preservation of fruits and vegetables, and no objection has been made to this practice; but in more recent times, and since preserved food has come into more general use, the practice of using other sub stances has also largely increased. The ques tion whether the use of such articles for this purpose may be injurious to the health of the consumer does not appear to have been yet satis factorily settled. The experiments of Tunni cliffe and Rosenheim would appear to show that food mixed with boric acid and borax, taken separately and together in such quantities as are ordinarily employed, may be eaten with im punity, but earlier observers have arrived at contrary conclusions. On account, therefore, of the possibility of the use of such chemicals in the preservation of food by persons wholly unacquainted with their physiological properties, legislation appears to be tending in the direction either of prohibition of the use of chemical preservatives or of regulating their use by mak ing their presence known to the consumer. Many substances have been experimented upon with reference to their preservative quality, among which are sulphur dioxide, sulphites and bisulphites, boric acid and its compounds, fluorides, chlorides, alum, lime, sodium carbon ate, formaldehyde, benzoic and salicylic add and their compounds. At the present time ben zoate of soda, boric acid, salicylic acid and formaldehyde appear to be most frequently used.
Benzoic Acid and Benzoates.—The chemical preservatives used most extensively are ben zoic acid and benzoate of soda. For a time they were the subject of heated discussion. The Bureau of Chemistry decided from extended experiments that these chemicals were harm ful, and recommended that they should be for bidden. The manufacturers who were using them in large quantities made a strong pro test against this prohibition, and the "Referee Board" of distinguished physiological chemists were appointed to make independent tests, and report to the Secretary of Agriculture. This board in 1909 reported that sodium benzoate in doses)) up to one-seventh of an ounce daily did not exert any recognizable deleterious effect upon health, and that this chemical up to that amount could not be classed as a poison within the meaning of the Pure Food and Drug Act; and also that the admixture of such small quantities of sodium benzoate with foods did not injuriously affect their food values. The regulations of the government based on this report permit the use of not more than one tenth of 1 per cent of benzoate as a preserva tive in manufactured foods, but require that its presence in the food be plainly stated on the label. In order to consume the maximum daily "dose' of one-seventh of an ounce it would be necessary to eat daily a quantity equivalent to nine pounds or five quarts of food so preserved.
Boric acid is most often used for the preser vation of meats, certain kinds of fruits and cat sup, and upon 'hams and fish. The latter are found to keep longer if the boric acid is rubbed over the outside. Two grams per kilo is suffi dent for fish. According to Le Fere boric acid
is eliminated slowly from the system, having been detected in the urine 40 to 50 days after it had been taken. It does not appear to interfere seriously with digestion so far as could be con cluded from experiments. Cases of flesh poison ing have been reported from Switzerland, where meat had been preserved with borates, which had not acted sufficiently as preservatives, but had only masked incipient putrefaction. An in vestigation of the United States Department of Agriculture showed that borax and boric acid in daily doses of 800 grains will be borne by most systems for a limited period. But when used continuously or in large quantities it in terferes noticeably with digestion and the gen eral health.
Sulphurous acid and its compounds have been used to some extent for the preservation of food, but not so much at present as formerly. These compounds and especially sulphur di oxide have a powerful germicide action. Au thorities differ as to their physiological action. Polli found that 8 to 12 grams of sulphurite were not injurious to adults. Ostertag, Ber natzik and Braun found that one gram of magnesium sulphite caused disorders of the stomach in women. Fischer found that 50 per cent of the preserved meat products sold in Breslau in 1895 contained sulphites, the quan tity of sulphur dioxide varying from .34 to .01 per cent. According to Riche, sulphurous acid and its salts, especially calcium bisulphite, have a considerable action on meat, altering its normal condition. This action causes changes in the soluble proteid substances. An addition of 1 per cent of a sulphite to meat is not per ceptible to taste or to smell. On cooking the meat the sulphite is only partially decomposed and expelled. Fischer states that meat con taining more than 0.1 per cent of sulphur di oxide shbuld be regarded as injurious to health. The United States Bureau of Chemistry in its Bulletin 84 shows that the sulphurous add compounds produce serious disturbance of the bodily functions and injury to' digestion and general health; imposing an unusual burden of work upon the kidneys.
Salicylic acid is one of the constituents of many of the modern meat preservatives. Bersch placed a portion of the flesh of a recently slaughtered animal in a concentrated aqueous solution of salicylic acid, and found that after four days the exterior Of the meat was perfectly sound, but the interior showed signs of putre faction, and contained many micro-organisms. He, therefore, concluded that the preservation of fresh raw meat by salicylic acid was not practicable. In, such meat compounds as sau sages and potted meat, where the salicylic acid. is uniformly distributed through the mass, its germicidal properties would obviously exert a more decided action. On account of its decided taste it cannot be used so freely in meat prepa rations as in other kinds of food in which the taste of the preservative is concealed. Here again authorities differ as to the action of this preservative on the human economy, when used in connection with food substances. The Paris Academy has forbidden even the least addition of salicylates to food, on account of their lia bility to injure the kidneys or digestive organs, when any weakness of these organs exists.