CHAPTER IX. 

 GLUCOSE. 



FINAL DETERMINATIONS OF OSMOTIC PRESSURE. 



The conditions under which the determinations recorded in this 

 chapter were made were the same as for the " final" measurements of 

 the osmotic pressure of cane sugar. There was no sensible change in 

 the rotation of the solutions while in the cells; and there was, therefore, 

 no gain or loss in their concentration. The temperature maintained 

 in the baths was constant to within 0.02°, except when some unforeseen 

 accident happened to the regulating system. It has already been 

 stated that the usual cause of such accidents is a temporary failure of 

 the current at the power house. If this is promptly discovered, serious 

 results may be avoided by switching the regulating devices to the 

 storage battery. The normal effect of a break in the current is, of 

 course, a drop in the temperature of the baths. Occasionally, the 

 temperature of the baths is forced up above that for which the thermo- 

 stats are set, but this is always due to a failure to make the "cooling 

 margin" sufficiently ample to cover all possible fluctuations in external 

 temperature conditions. In practice it rarely happens, except when 

 measuring osmotic pressure near the temperature of the outside air. 

 Whenever a deviation in bath temperature has been sufficient to produce 

 a really serious thermometer effect, the fact has been made apparent in 

 this report by omitting from the record the readings of the day or days 

 through which the thermometer effect persisted. 



The material employed for the determinations was the same as that 

 used for the measurements reported in Chapter VII. 



It was intended originally to begin the "final" measurements of the 

 osmotic pressure of glucose solutions at 0°, and then, as in the case of 

 cane sugar, to repeat the work at each higher interval of 5° or 10° in 

 regular order. But the disaster to the cells explained previously made a 

 change in plan advisable. It was desired to resume and complete the 

 work on cane sugar at high temperatures with the least possible loss 

 of time; and to this end the deposition and development of the mem- 

 branes in the new cells were begun at the highest practicable temperature, 

 namely, 30°. But as the new cells, after serving at high temperatures, 

 might also be lost on returning to ordinary or low temperatures, it was 

 decided to measure the osmotic pressure of glucose at each temperature- 

 interval for which the membranes must be developed before resuming 

 the work upon cane sugar. In other words, it was decided, after 



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