CHROMIC ACIDS, MERCURY SALTS. 65 



these in acetic and sulphuric acids. The results of quan- 

 titative analyses by the methods given are unreliable 

 when formalin is present, and hence it is a question if this 

 is the best material to be used even in preserving milk 

 samples that are to be kept some time before being an- 

 alyzefl. (Thompson, Alerkel, Kruger.)* 



VI. CHRo:\nc acid and other preservatives. 



Chromic acid, potassium bichromate, as well as am- 

 monium salts and mercury salts, and ammonia, all serve 

 as preservatives of milk samples, but for obvious reasons 

 are used only in samples to be analyzed ; 0.25 gram of 

 potassium bichromate is sufficient to prevent the coagu- 

 lation of 250 c. c. of milk for two months. Chromic acid 

 is used as a 20 per cent aqueous solution. One drop of 

 this in 100 c. c. of milk will keep the latter fresh for eight 

 days ; 25 per cent ammonia produces a similar effect. 

 The preserving power of any of these substances is large- 

 ly dependent upon the temperature of the milk. In no 

 case should it be allowed to rise above 10 degrees C. The 

 results of comparative tests before and after treatment 

 with these preservatives have shown that in the deter- 

 mination of fats, etc., these substances do not interfere. 



*"E.xpei"ience of late years in laboralory and anatomical work 

 has abundantly shown that formaldehyde hardens al- 

 buminous matter and converts it into a substance with a leathery 



appearance Gottslein (Deut. Med. W'ach, XXII. 



797) determined that such food products when hardened by the 

 use of formaldehyde cannot again be softened by boiling." — Dr. 

 Young. Secretary of State Boartl of Health of Elaine. 



The Cornell Experiment Station bulletin Xo. iiS states: "The 

 behavior in the Babcock test of milk which has been preserved 

 by formalin shows that its composition is in some way affected. 

 When formalin is used the curd often fails to dis- 

 solve (in sulphuric acidl and becomes a hard compact mass." 



For the effect of formaldehyde on the proteids of milk see also 

 .■\nnalen der Chemie, Vol. 310. p. 25 (iSiio): Zeitsch. fur Physiol. 

 Chem., 2J, l-'7 (i8u(i): \'ermont Experiment Station nth .A.n^ 

 nual Report, page 353. — Translators. 



