THE MILK CONTRACTOR 335 



processes of clarifying and pasteurizing but that most of the loss is properly 

 placed under the other heads in the following list of losses and should be 

 eliminated : 



1. Leaky cans. 



2. Dented or battered cans. 



3. Partially filled cans. 



4. Careless handling of the cans in transferring them from the cars 

 and in dumping them. 



5. Insufficient draining of the cans. 



6. Leaky or battered apparatus. 



7. Fillers in disrepair leaky valves. 



8. Losses at the filler from poorly adjusted valves, careless handling, 

 breakage of bottles, etc. 



9. Loss arising from failure to remove all the milk from pasteurizers, 

 pipes, pumps, tanks and other apparatus. 



10. Mechanical losses, and loss by evaporation in clarifying, pasteur- 

 izing and cooling. 



Homogenized Milk. Many city milk dealers, besides selling whole 

 milk and cream, put out homogenized milk and milk beverages. The 

 former is a comparatively new product. According to Baldwin the 

 patents on the first machine were taken out by Gaulin in 1892, but the 

 present successful type was not perfected till 1902. Milk and other 

 emulsions are homogenized by forcing them through very fine openings 

 under pressure of about 3,000 Ib. per square inch with the result that the 

 fat globules are broken up into fragments so minute that they cannot ag- 

 glutinate and cannot rise because, as Lindet has shown, the ascending 

 force of the fat globules in milk and cream is proportional to the cubes 

 of their radii and so when the diameters become less than 1 or 2 microns 

 milk will not cream. 



Homogenized cream can neither be whipped nor churned to butter. 

 In this country two machines are in common use for homogenizing milk, 

 the Gaulin and the Progress homogenizers. In the Gaulin machine the 

 milk is forced by single-acting pumps against an agate valve which presses 

 against a ground seat and forces the milk between the ground surfaces of 

 the valve and seat. In the Progress machine the milk is forced by single- 

 acting pumps between a series of discs with ground surfaces. The discs 

 are placed flat on one another, are held together by a rod running through 

 the center and are enclosed in a cylinder. The discs are pressed against 

 each other by a heavy spiral screw which regulates the pressure to which 

 milk is subject. The milk passes from the center to the periphery of the 

 discs of which there are two types. One of them has very fine grooves 

 through which the milk shoots against a hard shoulder and the other has 

 smooth surfaces with narrow area of contact. Owing to the high pres- 

 sure under which the machines work, considerable skill is needed to oper- 



