378 THE CHEMICAL CONTROL OF THE DAIRY. 



added (2 drops per 100 c.c.), and no correction is necessary for 

 so small a quantity. 



Siegfeld finds that the presence of much formaldehyde in milk 

 has a tendency to increase the amount of fat by the Gerber 

 method. This may be obviated by adding 1 c.c. of hydrogen 

 peroxide, or better, 0-5 of a 40 per cent, solution of hydroxyl- 

 amine hydrochloride per 100 c.c. of milk, and correcting for 

 increase of volume. 



The formaldehyde, however, combines with the protein, and 

 raises the apparent percentage of total solids and solids not 

 fat. Bevan has also suggested that the milk-sugar is hydrolysed 

 into dextrose and galactose, as he found the increase in total 

 solids more than the total amount of formaldehyde added ; but 

 this has been disproved by Hoft. 



Potassium Bichromate, Mercuric Chloride, and Solid 

 Antiseptics. These add considerably to the weight of the 

 total solids and solids not fat, and cannot, therefore, be recom- 

 mended. If fat only is to be determined they are efficient. 

 Siegfeld does not consider that the analysis of samples preserved 

 by potassium bichromate is trustworthy. 



Sterilisation may be resorted to. Certain changes take place, 

 which do not usually interfere with the analysis. The cream 

 rises and clots on the surface, and it is not easy to obtain an 

 average sample. 



Cold Storage. Samples may be frozen and kept in a cold 

 chamber, if one is available ; they keep for an indefinite period 

 thus, but require carefully remelting and remixing. This 

 method, which is not always available, is superior to all others, 

 and should be resorted to in those dairies which possess a freezing 

 plant and cold storage room. 



The Control of Milk during delivery to Customers. 



A very important part of the work of the dairy chemist is the 

 control of the men employed in delivering milk. It is evident 

 that a man on a milk round, being under no supervision for a 

 greater part of the time, has ample opportunities, should he be 

 so disposed, to adulterate or " lengthen " the milk of which he 

 has temporary charge. He may also, with the best intentions 

 possible, unwittingly deteriorate the quality of the milk by 

 allowing the cream to rise on the milk, and serving some cus- 

 tomers with the richer portion, thereby leave a poorer quality 

 for others. For the purpose of this control it is necessary to 

 take three series of samples. 



(1) Samples representative of the mixed bulk of milk that is placed in 

 charge of the man. 



(2) Samples taken in the streets in the course of delivery. 



(3) Samples of the small quantities of milk returned. 



