548 CCi- POSITION OF CREAM. 



The abov« remarks apply to milk of ordinary quality and consistency. 

 In ve^y thin ?r poor milk, in which little cheesy matter is contained, the 

 cream will rise more quickly. 



2°. Measurement of cream — the galactometer. — The richness of milk 

 is very generally estimated by the bulk of cream which rises to its 

 surface in a given time. For the purpose of testing this richness, a 

 simple instrument, dignified by the learned name of a galactometer 

 (milk-gauge), has been recommenJed and may often be useful. It con- 

 sists of a narrow cylindrical vessel or long tube of glass, divided or gra- 

 duated into 100 equal parts. This vessel is filled up to 100 with the 

 milk to be tested, and at the end of 24 or 36 hours, the quantity of cream 

 which has risen is estimated by the number of degrees of space which it 

 occupies at the top of the milk. If it cover 3 degrees the milk yields 

 3 per cent., if 7 degrees 7 per cent, of cream. This instrument, how- 

 ever, will give a result which will be generally less than the truth, be- 

 cause the cream will always rise slowly through 5 or 6 inches of milk — 

 the smallest length which the instrument can conveniently be — and most 

 slowly in the richest and thickest milk. Unless considerable care be 

 taken, therefore, this milk-gauge may easily lead to erroneous con- 

 clusions in regard to the relative degrees of richness of different samples 

 of milk. 



3°. Composition of cream. — Cream does not consist wholly of fatty 

 matter (butter), but the globules of fat as they rise bring up with them a 

 variable proportion of the casein or curd of the milk, and also some of the 

 milk sugar. It is owing to the presence of sugar that cream is capable 

 of becoming sour, while the casein gives it the prop*erty of curdling when 

 mixed with acid liquids or with acid fruits. 



The proportion of cheesy matter present in cream depends upon the 

 richness of the milk and upon the temperature at wliich the milk is kept 

 during the rising of the cream. In cool weather the fatty matter will 

 bring up with it a larger quantity of the curd, and form a thicker cream, 

 containing a greater propouion of cheesy matter. The composition of 

 cream, therefore, is very variable — much more so than that of milk — 

 and depends very much upon the mode in which it is collected. 



A specimen of cream, examined by Berzelius, which had a density 

 (specific gravity) of 1*0244, consisted of — 



Butter, separated by agitation 4*5 per cent. 



Cheesy matter, separated by coagulating the butter- 

 milk 3-5 " 



Whey 92-0 



100 

 Some of the butter remained, as is usually the case, in the butter- 

 milk, and added a little to the weight of the curd which was afterwards 

 separated, but the result of this analysis is sutlicient to show that cream 

 in general contains a very considerable proportion of cheesy matter- 

 sometimes almost as much cheese as butter.* 



* The clouted cream of Devonshire and other Western counties, as well as the butter pre- 

 pared from it, probably contains an nnusually large quantity of cheese. It is prepared by 

 straining the warm milk into large shallow pans into which a little water has previously been 

 put, allowing these to stand from 6 to 12 hours, and then carefully heatin, them over a slow 

 fire, or on a hot plate, till the milk approaches the boiling point. The n Jlk, however, muat 



