188 NORMAL MILK : ITS ADULTERATIONS, ETC. 



great delicacy as the former ones, and may not be obtained with 

 milk containing only a small amount. 



(4) Heat some of the milk for thirty minutes on the water 

 bath with a little sulphuric acid and a drop of dimethylaniline ; 

 filter ; render alkaline with caustic soda ; and boil till the smell 

 of dimethylaniline has disappeared. Filter ; moisten the filter 

 paper with acetic acid, and sprinkle lead peroxide on it. A blue 

 colour is developed if formaldehyde is present. 



(5) To the distillate add a 3 per cent, solution of anihne. 

 Formaldehyde produces a white precipitate, which is dissolved 

 on boiling, but is deposited again on cooling. 



(6) To 5 o.c. of the distillate add 1'5 c.c. of a 2 per cent, solution 

 of phenylhydrazine hydrochloride, 4 drops ferric chloride solu- 

 tion, and 12 drops sulphuric acid. A rose or dark red colour 

 is produced in the presence of formaldehyde. 



A preservative containing a nitrite in addition to formaldehyde 

 has been put on the market ; the nitrite masks the formaldehyde 

 reactions, but Monier- Williams has pointed out that if this is 

 destroyed by the addition of a little urea, the tests for formalde- 

 hyde may be obtained. 



Hydrogen peroxide is employed as a preserving agent ; Budde 

 has patented a process which consists in adding hydrogen per- 

 oxide to milk, and heating to 50° to 55° C. to complete the 

 liberation of the oxygen by the catalase of milk. It appears 

 to act by liberating oxygen in the interior of the micro-organisms 

 present, and thus bursting them. 



If a milk is found to contain abundance of soluble albumin, 

 and not to give the para-phenylene-diamine or ortol reactions 

 {p. 195), it is probable that it has been treated by Budde's 

 process. 



Hydrogen peroxide may be detected in milk by adding to a 

 small quantity of fresh milk a little ortol, and adding an equal 

 bulk of the suspected milk. In the presence of hydrogen per- 

 oxide a red colour will be produced. 



A preservative consisting of a solution of hydrogen peroxide 

 in brine and pellets of potassium carbonate and citrate has been 

 put on the market ; sodium peroxide and perchlorate are also 

 used. 



M. Wynter Blyth has devised the following method for deter- 

 mining the presence of preservatives in milk : — 



(1) Measure 10 c.c. of each milk into clean wide test tubes. 



(2) Measure 10 c.c. of a sterile milk known to be free from 

 preservatives into a test tube (these control tubes can be kept 

 ready for use). 



(3) Add to each milk 2 c.c. of a very strong slightly alkaline 

 solution of litmus. If any tube is not the same shade of blue 



