384: Transactions. — Chemistry. 



Art. LXL — On the Evolution of Heat during the Hydration of Clay-slate, 



Clay, and Coal. By William Skey, Analyst to the Geological Survey 

 of New Zealand, 



[Read before the Wellington Philosophical Society, 29th August, 1874.] 



Having announced, in November, 1871,* that clay-slate hydrates when in 

 contact with water, as shown by the coagulation test devised by me, I have 

 been desirous to obtain corroborative evidence in support of this statement, 

 and so prosecuted the matter further ; and being under the impression that 

 the hydration of this substance would evolve heat, I ground some clay-slate to 

 a very fine powder and put it in a small quantity of distilled water, when 

 an elevation of temperature occurred in the mixture equal to about 2° F. above 

 the temperature of the materials used. 



To make sure that none of this rise was due to heat generated during the 



act of crushing, and retained in such a manner that the exact temperature of 

 the powdered substance could not be ascertained, I repeated the experiment, 

 but with this variation — the crushed slate was bottled off and not used till 

 twenty-four hours afterwards. The thermometric results were the same. 



The water after the mixing was slightly alkaline, owing no doubt to the 

 presence of a minute quantity of alkalies derived from the slate, to the 

 hydration of which or their compounds a part of the elevation of temperature 

 noticed might have been due. To obtain, therefore, some indication of the 

 quantity of this, I crushed some glass to quite as fine a powder as I had the 

 slate instanced, allowed it twenty-four hours to cool (as I may state here I have 

 for all succeeding experiments upon substances dried by heat), and then mixed 

 it with water in same proportions as observed for the slate, when an elevation 

 of temperature barely equal to 1° F. occurred. The water was of course 

 strongly alkaline directly after the mixing ; clearly, therefore, the alkalies of 

 the slate had no important share in producing the elevation of temperature 

 observed. 



At this stage I struck aside a little to experiment upon coal, clay, and 

 other substances, in the hope of obtaining facts extending over a wider field, 

 and so capable of being handled more correctly and with greater ease, and I 

 found carbonate of lime, as also quartz and brown coal or clay, did not give 

 any indication of an evolution of heat when mixed with water; steatite, 

 however, and anhydrous coal, also hydrous coal, clay, and lignin, when dried 

 gently or wholly, did so. Steatite had as much heating power as slate, while 

 all the remaining substances cited were superior to it in this respect. In the 

 case of naturally anhydrous coal, or hydrous coal and clay dried at from 90° to 

 212°, or over desiccating substances (at common temperatures), I frequently 

 obtained a rise of temperature from 3° to 6° F. 



* Proceedings of New Zealand Institute, vol, iv., p. 381. 



