COLORADO EXPERIMENT STATION 
17 
angle and at the same time revolved so that the acid may wash down 
all adhering cream on the inside of the neck of the bottle. Acid should 
not be allowed to fall directly into the cream, as such a practice may 
cause black particles to appear in the fat column. There is also danger 
of the neck choking up and the acid overflowing on the operator’s 
hands. 
The contents should then be mixed by a gentle rotary motion, 
avoiding spilling or shaking curd particles into the neck of the bottle. 
The sample should then turn a dark chocolate color. After mixing, each 
bottle should be allowed to stand a short time, until the desired uni¬ 
form chocolate color is obtained. 
Commercial sulphuric acid of a specific gravity of 1.82 to 1.83 
should be used. Such acid should not be left in an open container, as the 
action of the air will very soon cause it to become weak and unfit for 
use. 
Rich cream will require a little less acid than thin cream, and sour 
cream will require a little less than.sweet cream. 
Whirling .—The tests having been let stand after mixing with the 
acid, as described above, a second gentle rotary motion should be given 
and hot, soft water of 170 degrees F. added in proportion to the amount 
needed as indicated by the color of the mixture, usually up to the neck 
of the bottle. Balance in tester and whirl at the proper speed of tester 
for five minutes. 
Stop the tester and add soft water, 170 degrees F., to within three 
or four graduations of the top of the graduated scale on the neck of 
the bottle. Unless a steam tester is used, care should be taken to keep 
the tests at 170 degrees F. by inserting in a hot water bath of that 
temperature for five minutes. 
Whirl two minutes. 
All water added must be soft. If soft water cannot be obtained, 
hard water may be softened by adding a few drops of sulphuric 
acid before putting into the bottle. The use of hard water will cause 
air bubbles on the top of the fat column. 
The periods of whirling given mean the time during which the 
tester is run at full speed, and do not include the time used in 
starting or stopping the machine. 
The following table gives the necessary number of revolutions for 
different size testers. 
Diameter of Machine 
No. of Revolutions per Minute 
10 1074 
12 980 
14 909 
16 848 
18 . 800 ' 
20 759 
22 724 
24 693 
