108 MANUAL OF MILK PRODUCTS 



graduation from to 50 occupies approximately 18 inches, it 

 is readily seen that closer reading can be made than with 

 the 9-gram six-inch 50 per cent cream bottle the scale of 

 which occupies approximately 2f inches. 



" In order to aid in reading the burette, the per cent lines on 

 the 18-gram scale extend entirely around it. By means of 

 these lines the operator can easily bring his eye to the level of 

 the liquid, which is a matter of great importance when accurate 

 work is desired. Such a burette can be constructed so that the 

 capacity of the bore is a definite number of cubic centimeters, 

 or that it will deliver a definite number of cubic centimeters, 

 allowing a certain number of seconds, say ten, for the alcohol 

 to flow down the sides. The first way is preferable when mer- 

 cury is used as a calibrating reagent, but as this reagent offers 

 many difficulties, it is better to construct the burette on the 

 basis of its delivery, allowing a certain period of time to elapse 

 before taking the readings." 

 Reagents used in calibrating. 



" For calibrating purposes denatured alcohol is very suitable. 

 In accurate work it is well to color this dark so that the meniscus 

 is not visible. This can be done by dissolving a small quantity 

 of black dye in cold water and then boiling the mixture for five 

 or six minutes until all the dye is dissolved. When cool, a 

 sufficient amount of the solution can be added to the denatured 

 alcohol so that the meniscus is not visible." 

 Hoiv to use the burette. 



" To calibrate glassware with the burette it is necessary to fill 

 the test bottles with the colored alcohol exactly up to the zero 

 mark. This can be readily done where a number of bottles 

 are to be calibrated by filling them approximately up to the 

 zero mark : within a short time the necks of the bottles will be 

 dry and then, by means of a medicine dropper, enough alcohol 

 may be added to bring the liquid exactly to the zero mark." 



In order to do accurate work with any burette where a pinch- 



