418 CREAM. 



exceed 0-0025 per cent. In Denmark and Germany, and in a 

 few dairies in England, filtration through layers of gravel and 

 sand has been practised, though the method appears to have 

 died out ; this method, which adds considerably to the labour 

 of handling the milk, owing to the necessity of washing the 

 gravel and sand with caustic soda, followed by water, sterilising, 

 and drying, fails to remove appreciably more from the milk than 

 simple straining or upward filtration through muslin or swans- 

 down. 



Another method which is considerably used is filtration through 

 a thin layer of cotton wool ; this method is fairly efficient, especi- 

 ally if practised as soon as possible after milking, and before 

 the particles of dirt have had time to disintegrate and yield 

 their soluble matters and micro-organisms to the milk ; a special 

 advantage of this method is that the cotton wool is very cheap, 

 and it is impossible to wash it, and, therefore, it is thrown away 

 and not used a second time. 



Fig. 48. Cream. 



The separator is also used as a cleaner for milk ; for this 

 purpose the separated milk and cream are either all made to come 

 out of one outlet or they are mixed immediately after separation. 

 This method is, of couise. perfectly efficient in removing solid 

 impurities, but it necessitates the milk being warmed and after- 

 wards cooled, and makes the milk very frothy, and may even 

 lead to incipient churning. 



Cream Composition. The name cream is given to the 

 layer which rises to the surface when milk is allowed to stand. 

 This layer consists essentially of the fat globules, together with 

 a proportion of the aqueous portion of milk (Fig. 48). 



