SUGARS. 67 



Bugar ; but it must be remembered that milk sugar fer- 

 ments slowly and with difficulty. In its application, all that 

 is necessary is to add a few drops of fresh yeast, and keep 

 the suspected liquid for a few hours at a temperature of from 

 80 to 100 Fahr. The mixture should be placed in some appa- 

 ratus by which the gas which forms may be collected and an- 

 alyzed. To effect this, we may till a large test tube and invert it 

 in a small shallow vessel ; or if there be but a, small quantity of 

 liquid, we may use a very simple and convenient apparatus 

 described by Bernard. This is simply a large test tube fitted 

 with a good cork, perforated to allow the passage of a small 

 tube which extends to the bottom. This tube may be turned 

 up at the lower end, and bent above so as to permit the 

 escape of the liquid as the gas is formed. The whole is com- 

 pletely filled with the suspected solution, to which have been 

 added a few drops of fresh yeast, and kept at a temperature 

 of 80 to 100 Fahr. If sugar be present, bubbles of gas will 

 soon begin to appear, which will collect at the top and force 

 a portion of the liquid out by the small tube. If no gas has 

 appeared at the end of four or six hours, it is certain that no 

 sugar is present. This test is conclusive, if proper care be 

 taken in its application ; and to insure accuracy, it is well to 

 test the yeast with a saccharine solution to demonstrate its 

 activity, and test it also with pure water, to be sure that it 

 contains no sugar. "We may then demonstrate that the gas 

 produced is carbonic acid by removing the cork and inserting 

 a lighted taper, which will be immediately extinguished, or 

 passing it into another vessel and agitating with lime-water, 

 which will be rendered milky by the formation of the insolu- 

 ble carbonate of lime. The alcohol remains in the liquid, 

 from which it may be separated by careful distillation. 



Measures for demonstrating the composition of the gas 

 and the presence of alcohol in the liquid are by no means 

 necessary in the ordinary application of the test. The dis- 

 tinct formation of gas in the liquid is generally sufficient 

 evidence of the presence of sugar. 



