niteiy in an ice box if a little toluene is kept on its surface to prevent 

 the growth of micro-organisms, and is exceedingly active in inverting 

 cane sugar. The invertase solution does not reduce Fehling's solution. 



THE KEEPING QUALITIES OF THE INVERTASE SOLUTION. 



The stock solution of invertase prepared as described keeps per- 

 fectly. A quantity of it has been tested during a period of fifteen 

 months and no change in its general appearance or inverting activity 

 was noted. Three other preparations of less age have also shown no 

 appreciable change. All of these solutions have been kept in an ice 

 box, and toluene was added in excess of saturation in each case. 

 Another preparation has been observed by- H. S. Paine, of this Bureau, 

 who found that the preparation did not change in its inverting -activ- 

 ity during a period of three months. This sample was kept at room 

 temperature (20 to 30 C.) during the day and in an ice box at night, 

 thus duplicating the conditions which occur where many analyses are 

 carried out each day with the use of the invertase solution. 



THE ROTATORY POWER OF THE INVERTASE. 



The stock solutions of invertase have a slight rotatory power, and 

 in a 400-mm tube they give a dextro-rotation of 1.0 V. In the 

 method to be described further on the inversion of 95 cc of sugar 

 solution is accomplished by 5 cc of the invertase solution, and there- 

 fore the correction to be applied for the rotation of the invertase solu- 

 tion is 0.05 when the reading is made in a 400-mm tube or 0.025 

 when a 200-mm tube is used; For all ordinary work these corrections 

 are negligible, but they can always be exactly determined when accu- 

 racy requires their use. 



NUMERICAL FORMULA FOR THE DETERMINATION OF CANE 

 SUGAR BY INVERTASE. 



If S denote the polarization of pure cane sugar before inversion and 

 /that after inversion, the numerical factor of inversion, which can be 

 found by experiment, is I/S. This factor varies greatly with the 

 temperature, due to the influence of the latter on the rotation of fruc- 

 tose. H. S. Paine and the author have measured this factor at 20 C., 

 when invertase is used as the inverting agent on sugar solutions of 7 

 per cent strength and have found its value to be 0.317; similar experi- 

 ments have given the factor 0.324 for the inversion by hydrochloric 

 acid when the solution is kept at room temperature over night and read 

 in the acid condition. For the same acid solution after neutralization 

 the factor 0.317 was found, showing that it is the acidity which causes 

 the difference between the factors for invertase and for the unneu- 

 tralized acid solution. To check this point, the same quantity of hydro- 

 chloric acid was added -to the solution which had been inverted by 



Cir. 50. 



