che;mistry — MORSE. 151 



which, by means of electrically driven pumps, the water (300 liters) is kept 

 in constant and uniform circulation, and the air in the enclosed space above 

 the water is made to pass continuously through pipes lying in the water. 

 By surrounding these baths with a thick covering of hair very slow changes 

 of temperature were secured despite considerable and rapid variations in 

 external temperature conditions. Nevertheless, we proceeded to devise 

 means for maintaining nearly constant temperatures in the space outside the 

 baths. For this purpose both electric and gas stoves were employed, and 

 for the latter there was devised a new form of gas regulator. Finally, to 

 regulate both the electric and the gas stoves, a new form of electric mercury 

 thermostat was constructed in which sparking — the usual difficult}^ with 

 this class of instruments — is suppressed by spanning the spark gap with a 

 resistance which bears a certain relation to the potential of the battery. 



A full account of the measures taken to eliminate the ' ' thermometer 

 effects," which had given us so much trouble in the earlier work, has been 

 published in the American Chemical Journal, volume xxxvi, and it is only 

 necessary to state here that they were entirely adequate for the removal of 

 the most serious obstacle to the accurate measurement of pressure which we 

 have encountered. 



With the improved facilities mentioned above, for the maintenance of 

 constant temperatures, a careful redetermination of the osmotic pressure of 

 cane-sugar solutions, ranging in concentration from o. i to i.o weight-normal, 

 was undertaken. This part of the work has been completed, and the results 

 have been published in the American Chemical Journal, volume xxxvi. 



The first series of measurements had led to the conclusion that : 



Cane-sugar, dissolved in water, exerts an osmotic pressure equal 

 to that which it would exert if it were gasified at the same tem- 

 perature and the volume of the gas were reduced to that of the 

 solvent in the pure state. In other words, dissolved cane sugar 

 exerts an osmotic pressure throughout the larger volume of the 

 solution equal to that which, as a gas, it would exert if confined 

 to the smaller volume of the pure solvent. 



It appeared important that this conclusion should be tested with the 

 utmost care, and great pains were taken to minimize or remove all known 

 sources of error. The measures which were employed with this end in view 

 have been fully discussed in the two published papers already referred to. 

 A tabular statement of the results is given on the next page. 



They appear to confirm in a convincing manner the conclusion which was 

 deduced from our earlier measurements of the osmotic pressure of cane-sugar 

 solutions. 



The measurement of the pressure of glucose solutions has also been under- 

 taken, and the first series of determinations is nearly completed. The results 

 indicate that the rule established for solutions of cane-sugar holds equally 



