33 



portion of clear liquid required being filtered out by means of Wiley's 

 tubes, already described. 1 These tubes are simply glass tubes about 9 

 to 10 inches long and J-inch caliber. At one extremity a slight riin 

 is made by turning back the edge while hot, and over this is stretched 

 and tied a piece of fine linen cloth. To use the tube it is inserted into 

 a beaker of water containing in suspension a quantity of very finely 

 ground asbestos ; by suction at the other end of the tube the linen cap 

 is covered with a film of asbestos and it is then immediately inserted 

 into the test-tube containing the hot precipitated Fehling solution; suc- 

 tion is again made on the tube and the portion of clear liquid obtained 

 is run into a porcelain dish containing the test solution by simply in- 

 verting the tube. These tubes may be cleaned and used over and over 

 again by washing off the asbestos film, dissolving out any sub-oxide of 

 copper which may remain in the cloth by soaking in nitric acid and 

 rinsing in water until they no longer taste acid. One covering of linen 

 suffices for many tests, and when worn out it is easily replaced. 



Working in this way a large number of samples can be analyzed in a 

 day, twenty-five to thirty being generally a fair day's work for opera- 

 tors on the stations of the Department of Agriculture, both sucrose and 

 glucose being determined, and also the total solids (from the specific 

 gravity), and this number is much exceeded in case of stress of work 

 by allowing the polarizations to stand until night, using all the daylight 

 for glucose determinations. By having a boy measure out the samples 

 and prepare them for analysis the amount of work done can be nearly 

 doubled. 



It remains to calculate the results obtained, and to facilitate this cal- 

 culation I have compiled the following table. In it will be found the 

 specific gravity and degree Brix, 2 and opposite to them factors for the 

 calculation of sucrose and glucose in juices of the corresponding spe- 

 cific gravity, according to the method of procedure given above. Two 

 factors for sucrose are given, one for instruments using as a normal 

 quantity 26.048 grams, such as Soleil-Scheibler, and one for those using 

 16.3 grams, such as the Laurent. These factors are the quotients from 

 division of the normal quantity by 50 x sp. gr. To use them it is nec- 

 essary simply to multiply by the reading of the polariscope, the result 

 giving directly the per cent, of sucrose in the juice. The glucose factor 

 is simply the reciprocal of the specific gravity multiplied by ten. To 

 use it, it is divided by the number of cubic centimeters of the normal 

 solution (50 to lOOcc.) required to precipitate lOcc. of Fehling's solution, 

 which, gives the result directly in per cent, If the solution has been 

 diluted twice (50 to 200cc.), divide the factor by half the number of 

 cubic centimeters required; if one and one-half times (50 to 150cc.), by 

 one and one half times the number of cubic centimeters required. 



1 Bull, de TAssoc. des Chim. de Sucre, et de Dist, Apr., 1884. 



3 Taken from the tables of Mategczek, Scheibler, and Stammer, as given by Dr. 

 Tucker in his " Manual of Sugar Analysis." 

 19623 No. 15 3 



