126 Testing Milk and Its Products. 



the liquid is lost by the shaking. It is well to put the 

 tablets in the cylinder with water at night; the solution 

 will then be ready for use in the morning. Excepting 

 a flocculent residue of inert matter, " settlings/ 7 which 

 will not dissolve, the tablets must all disappear in the 

 solution before this is used. The strength of the tablet 

 solution does not change perceptibly by standing, at 

 least for one week. The only precaution necessary is 

 to avoid evaporation of the solution by keeping the cyl- 

 inders tightly corked. The solid tablets will not change 

 if kept dry, any more than dry salt changes by age. 



141. Accuracy of the tablets. The tablets have been 

 repeatedly tested by chemists and found to be accurate 

 and very uniform in composition. Tests made with the 

 tablets according to the directions here given can there- 

 fore be relied on as correct. The alkali solution is very 

 sensitive, however, and should not be measured in a cyl- 

 inder which has been previously used for measuring 

 sulfuric acid, as the smallest drop or film of acid from 

 a dish or from the operator's fingers will change the 

 standard strength of the tablet solution. Of late pow- 

 dered sodium carbonate weighed out exactly in the 

 quantity required for making a gallon of tenth normal 

 solution has been placed on the market; these "test pow- 

 ders " are cheaper than alkaline tablets and when put 

 out by a reliable firm are equally accurate as these. 



142. Making the test. The cream to be tested is 

 thoroughly mixed, and 17.6 cc. are measured into the 

 cup. The pipette is rinsed once with water, and the 

 rinsings added to the cream in the cup. A few cc. of 

 the tablet solution prepared as given above are now 



