The BabcocJc Test. 67 



respectively. Comparing such a hydrometer with the Swedish 

 tester, the weight of the former would make it ten times as 

 sensitive as the latter, if the size of the stem was the same in 

 either case; as it is, the tester has the advantage in point of 

 thinness of stem (see 106), as the volumes of the same lengths of 

 stem in the two instruments are as the squares of their diam- 

 eter, i. e., as 25:36. This means that the Swedish testers are 



36 1 



only 1Q x ^ = 7 as sensitive as the hydrometer, or a difference 



on the scale of the latter amounting to 15.5 mm. (see above), 

 would represent only 2.2 mm., on the scale of the Swedish 

 tester. The line marked Too strong must therefore be only 1.1 

 mm. (2*3 of an inch) below the Correct line; and that marked 

 Too weak the same distance above the line. But this is too 

 small a distance to be differentiated by persons unfamiliar 

 with the use of delicate hydrometers, especially since the men- 

 iscus of the liquid formed around the stem of the tester renders 

 an accurate reading somewhat difficult. 



The Swedish acid tester can be made more delicate by changes 

 in one or two directions; by making the bulb larger, thus neces- 

 sitating an increase in weight, or by making the stem thinner. 

 By way of comparison it may be stated that the hydrometers 

 used for determining the specific gravity of the ether-fat solu- 

 tion in Soxhlet's areometric method of milk analysis have a 

 stem only 2 mm. in diameter, and the distance of the scale 

 between .765 and .745 is 70 mm., or 2| inches. 



Even if these testers are changed as suggested, their practica- 

 bility still remains an open question. The action of sulfuric 

 acid of different strength on milk is very characteristic (75) 

 and in the hands of experienced operators, is as delicate an 

 index to the strength of the acid as can be desired, making 

 rather unnecessary a separate instrument for ascertaining the 

 correctness of the strength of the acid used in milk testing. 



78. The color of the fat column an index to the strength 

 of the acid used. The strength of the acid is indicated 

 to a certain extent by the color of the fat which separates 

 in the neck of the test bottle when milk is tested. If the 

 directions given for making the test are carefully fol- 



