and Attached Water, 221 



peared that the greatest heat was developed when four parts 

 by weight of water were mixed with one of finely powdered 

 gum arabic ; a rise of l°'l ensued, namely from 15°- 7 to 

 16°*8. The first temperature was that of the water in the 

 outer of two concentric beakers, the inner of which contained 

 the gum. The beakers were thickly wrapped and covered 

 with flannel, and had been in such contact for several hours. 

 To the above numbers, however, I do not attach much quan- 

 titative value ; for, owing to viscosity, solution takes place very 

 slowly. The results, however, clearly show that the heat de- 

 veloped is far too small to counteract any great heat-absorp- 

 tion by solution, and that accordingly the latter does not exist. 

 The heat liberated is indeed scarcely more than the heat of 

 capillarity. 



I believe that most of us would have been disposed to pre- 

 dict that in order to boil a solution of gum a temperature 

 above 100° C. would be required. This was, I confess, my 

 own persuasion until I was enlightened by the above experi- 

 ments on the separation of water as ice from gum-solutions of 

 all strengths. But being so enlightened I was able to predict 

 that a solution of gum would boil at a temperature not above 

 100° C. A 20-per-cent. solution of gum arabic appeared to 

 boil in a test-tube over the bare flame below 100° C. But as 

 it is almost impossible to avoid a certain amount of decompo- 

 sition under these circumstances, a tube holding a fresh 

 quantity of the 20-per-cent. solution was placed in a wider 

 tube containing a solution of chloride of sodium which boiled 

 at 104° C. On heating the latter gradually the gum-solution 

 could be made to boil before the brine began to do so. And 

 if by rapid heating the latter were made to boil, the gum-solu- 

 tion boiled violently, and continued to do so after the brine 

 had ceased. A thermometer in the gum-solution showed 

 100° C. Further, a 40-per-cent. solution of gum arabic when 

 surrounded by boiling water boils at 98° C, or two degrees 

 lower than the water. 



§ 163. Albumen. — Dry albumen when mixed with ice can 

 only depress the temperature 0°*25 C. Four parts by weight 

 of water and one of albumen, both at 18°' 2, gave, on mixture, 

 a temperature of 19°*5. In another experiment the common 

 temperature rose from 19° to 21°. In the above experiments 

 commercial albumen was used. For more exact experiments 

 white of egg was used, which analysis showed consisted of 

 13-37 per cent, of albumen (dried at 100° C.) and 86*63 of 

 water. Such white of egg begins to separate ice at 0° C, and 

 freezes into a solid mass at — o, 5. A solution diluted to 

 5 per cent, begins to give up ice at 0° C, and is solid at 



