PEROXIDES. 211 



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. 216), 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. 



Werther's test consists in adding 10 drops of a 1 per cent, 

 solution of sodium orthovanadate in 10 per cent, sulphuric 

 acid to 10 c.c. of milk ; hydrogen peroxide gives a distinct red 

 coloration. 



A preservative consisting of a solution of hydrogen peroxide 

 in brine and pellets of potassium cabonate and citrate has been 

 put on the market; sodium peroxide and perborate 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 



N 

 as the control, add very carefully a solution of caustic soda 



2i 



drop by drop till the correct shade is obtained. 



(4) Plug all tubes with cotton wool, and heat them in a water 

 bath kept at 80 C. for ten minutes. 



(5) Cool the tubes, and add to each 0-5 c.c. of a solution con- 

 taining 0-5 c.c. of sour milk per 100 c.c., shake well, and let the 

 tubes stand for twenty-four hours at a temperature between 

 15 C. and 24 C., or until the control tube is white. 



If preservatives are absent the milk will become white at the 

 same time as the control ; in the presence of preservatives the 

 tubes will remain blue or pink. 



If formaldehyde is found a quantitative estimation may be 

 made by making up a series of tubes containing known amounts 



