54 Milk and Its Products. 
these there are two forms. In one there is a bulb 
in the middle of the neck, and graduations above 
and below. Ordinarily the lower graduations have a 
capacity of 5 per cent, the bulb a capacity of 10 
per cent, and the upper graduations a capacity of 
10 per cent. The use of this form of bottle re- 
quires that when the fat is read off the bulb should 
always be completely full, and the upper and lower 
surfaces of the fat rest on the upper and lower 
graduations respectively. Another form of cream 
test bottle has a neck much wider than that used 
for ordinary milk testing. Bottles of this form have 
a capacity up to 35 per cent, or even more. The 
graduations are usually not closer than .5 of 1 per 
eent. This form does away with the awkwardness 
of the bulb in the center, but it is not possible 
to read the column of fat to so small a_ fraction, 
usually to not less than .5 of 1 per cent. For 
testing cream, particularly cream that is rich in fat, 
a special pipette is necessary. The specifie gravity 
of cream containing 25 per cent of fat or over is 
nearly that of water, and in testing cream of this 
quality a pipette of 18 instead of 17.6 cubic cen- 
timeters capacity is used. For testing skim-milk, 
where it is desirable to read the small fractions of 
1 per cent, two forms of bottles have been devised. 
In one, two pipettes full of milk are used, and the 
graduations have one-half the ordinary value; in the 
other form, the bottle has two necks, one of ordi- 
nary width for the introduction of the milk and acid, 
and the other an extremely narrow one, in which 
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