3^6 TRANS. ST, LOUIS ACAD. SCIENCE. 



the thermometer rose, a constant and rapid evohition of gas was 

 observ^ed. As this did not in character resemble an evolution of 

 steam, an examination was made, and it was found to be due to 

 Carbon Dioxide. When a solution of like strength was placed in 

 the brine-bath the thermometer rose to ioo° C. and the phenome 

 non was entirely different. It was then actually boiling. There- 

 fore we conclude that the boiling-point of this solution of Gum 

 Arabic is the same as that of water. 



GELATINE. 



A 50 p. ct. solution of confectioner's gelatine did not evolve a 

 bubble of vapor when subjected to the heat of a water-bath, al- 

 though the temperature rose to 99°. 8. In a brine-bath, however, 

 the solution did boil, and the thermometer immersed showed a 

 constant temperature of 100° C. 



Determinations of vapor tension of the same solution at 100° 

 C. showed it to be less than that of water at the same tempera- 

 ture by 2-3 mm. mercury. Consequently the boiling-point must 

 be slightly above that of water. This is in acordance with the- 

 ory. Under no circumstances can gelatine solutions boil lower 

 than water. Let us consider that dissociation of the solution does 

 take place at 97° C. The wa'er liberated can only have the ten- 

 sion of water, which at that temperature is less than the baro- 

 metric pressure, and therefore a phenomenon of boiling cannot 

 be observed. 



We need not enter into detail of description concerning experi- 

 ments on Gum Tragacanth, Agar Agar, Dextrine, and Starch. 

 The results were in every instance the same in character as those 

 obtained for Gum Arabic and Gelatine. They aie all in agree- 

 ment with our thermo-chemical results, and contradictory of Gu- 

 thrie's results. 



II. — Tlie dissociation of Oelatiiie and Cwiini Arabic Hydrates at low 



temperature. 



Gelatine hydrates containing 50, 60 and 75 p. ct. of water were 

 cast in cylindrical form, and cavities formed in the axis of each 

 for the reception of thermometers. They were subjected to — iS° 

 C. for several hours, when they presented no signs of being frozen. 

 The same hydrates were subjected to the same temperature as 

 above on slides, and examined under the microscope in polarized 



