298 FOOD AND FOOD ADULTERANTS. 



as it conduces to the preservation of the beer by destroying the germs 

 of unhealthy ferments, not by simply paralyzing their activity as an- 

 tiseptics do, and moreover it introduces no foreign constituents into the 

 beer. Liquid carbonic acid is also coming into use in some of the larger 

 Continental breweries. 



Other preservative agents extensively employed at the present day 

 are salicylic acid, bisulphite of lime, and boracic acid. 



SALICYLIC ACID. 



Salicylic acid (C 7 H 6 O 3 ) was first prepared by Piria and Ettliug by 

 oxidizing salicyl aldehyd, which had previously been obtained from 

 various vegetable sources. It was afterwards obtained from oil of wiu- 

 tergreen, which is nearly pure methyl salicylate, a constituent also of 

 mauy other essential oils. Its artificial production from phenol (car- 

 bolic acid) was discovered by Kolbe and Lauterrnann in I860 but was 

 not put into practical use until 1874, when Professor Kolbe succeeded 

 in producing it at a moderate cost. It is now prepared almost exclu- 

 sively in this way, the cheapness of the method having driven out of the 

 market that which is prepared from oil of wintergreen. 



By this process sodium carbolate is treated with dry carbonic acid 

 gas and distilled at a rather high temperature, when one-half of the 

 phenol combines with the sodium, forming sodium salicylate, while 

 the other half is distilled over. The residue is decomposed with hydro- 

 chloric acid, the salicylic acid filtered off and washed, and purified by 

 recrystallizatiou or sublimation. The purest salicylic acid is obtained 

 by dialysis, by which all the tarry matters can be separated. It is com- 

 posed of long acicular crystals, having a peculiar, pungent, sweetish 

 taste. It is irritating to the mucous membrance of the nasal passages 

 and produces sneezing when handled. 



The extended use of salicylic acid it owes to its property of arresting 

 the action of ferments. This property has been extensively in vest i 

 gated and it is unnecessary to go into the subject further here. 1 



In medicine, besides its use externally as an antiseptic, it is admin- 

 istered very extensively internally, its chief application being as a 

 remedy for acute rheumatic fever. Its physiological action is given as 

 follows in the United States Dispensatory, fifteenth edition, page 101 : 



When salicylic .acid la given to man in doses just sufficient to manifest its presence, 

 symptoms closely resembling those of cincbonisiu result. Tlicsu are fullness of the 

 head, with roaring and buzzing in the ears. After larger doses, to these symptoms 

 are added distress in the head or positive headache, disturbances of hearing and 

 vision (deafness, amblyopia, partial blindness), and excessive sweating. According 

 to Reiss (IlcrHnycr Klin. Wochenschrift, 1875, p. 674) decided fall of temperature, with- 

 out alteration of the pulse, also occurs; but this is denied by other observers. The 

 actions upon the system of the acid and of its sodium salts (also ammonium s;ilt. 

 Martenson, Petemb. Mf<l. Zrilxchrift, 1875, p. :54:5) appear to In- identical, and, :is sov- 



' For recent information on this subject reference may In- made (. n puper by .A. I!. 

 Griffiths, Chemical News .53, 28. 



