52 Testing Milk and Its Products. 



as the and 10 marks on the scale ascertained. This 

 modification was proposed by Louis F. Nafis & Co. , Chi- 

 cago. 



The lower section of this tester will displace 1 cc. of 

 liquid and raise it from to the 5 mark, but the tester 

 must be lowered slowly so that the upper section will not 

 come in contact with the liquid until the 5 mark is tested. 

 After ascertaining the correctness of this point, both sec- 

 tions are lowered so that the water rises above the top of 

 the upper section and the accuracy of the 10 mark is 

 also tested. 



58. The standard measure. In the place of an iron 

 nail, a piece of copper or glass rod may be advantage- 

 ously used as a standard measure. The standardization 

 is most conveniently done by weighing; since the specific 

 gravities of iron, copper and glass are 7.8, 8.9 and about 

 2. 7, respectively. Pieces of these materials replacing 2 cc. 

 of a liquid, will weigh 15.6, 17.8 and 5.4 grams, for iron, 

 copper and glass in the order given. 



A measure of the right weight may be suspended by a 

 very fine copper or platinum wire (melted into the glass 

 rod if this material be chosen), and is used directly for 

 calibrating test bottles as described above. Before a 

 measure so made is used as a standard, its accuracy should 

 be determined by weighing the amount of water at a temp, 

 of 17.5 C, which it replaces. The specific gravity of glass 

 especially, varies somewhat according to its composition, 

 so that a standardization of a measure by weight alone 

 cannot be depended upon always to give correct results. 



59. In submerging the measure in the test bottle to be 

 calibrated, care must be taken that all air bubbles are 



