W. Hallock — Chemical Action between Solids. 405 



the whole block puts an end to each experiment. As these ex- 

 periments were performed in summer there is scarcely a possi- 

 bility that the ice was colder than 0° C. 



Inasmuch as there seems to be an increasing inclination to 

 regard solutions and alloys as chemical compounds it seems 

 justified to speak of the action according to the alloy law as 

 chemical. On the other hand there are some cases which at 

 first appear as chemical action between solids which upon closer 

 investigation can be explained on a simpler assumption. 



For example, Mr. W. Spring* in a recent paper on this sub- 

 ject cites three particular cases as being chemical action be- 

 tween solids, the union of copper and sulphur, the reaction 

 between copper and mercuric chloride, and between potassium 

 nitrate and sodium acetate. 



The formation of the sulphide of copper, and other sulphides, 

 was accomplished by Mr. Spring by compression of the ele- 

 ments. But it is not even necessary that the sulphur and 

 copper be in contact. I have made the sulphide at ordinary 

 temperatures with the two an inch apart ancl a wad of cotton 

 in the tube between them. It is simply the vapor of sulphur 

 which attacks the copper. That sulphur gives off a perceptible 

 vapor at ordinary temperatures, especially in vacuo, is a fact any 

 one can easily demonstrate. The case of the copper and mer- 

 curic chloride is precisely the same. The vapo? 7 of the chloride 

 will go through a whole tube past cotton wads and attack the 

 copper (or color potassic iodide). Hence we can scarcely assert 

 that these reactions are between solid bodies. The reaction 

 between potassium nitrate and sodium acetate is equally uncon- 

 vincing. Mr. Spring expected an interchange of bases and 

 acids and left the mixture of the dry fine powders four months 

 in a desiccator to give time for the exchange. On removing 

 them from the desiccator a deliquescence was noticeable and he 

 therefore concludes that the interchange had taken place, since 

 the original salts do not easily deliquesce ; but the product of 

 the reaction (potassium acetate) does. It appears to me thus : 

 the moment the powders were brought to the air, the water 

 vapor enters the operation and we have, potassium nitrate, water 

 vapor, and sodium acetate, and the result of their mutual in- 

 teraction is a solution of potassium acetate and sodium nitrate. 

 In fact if the dry powdered salts are stirred together, in a very 

 few moments deliquescence begins, showing that whatever the 

 reaction it goes on at once, and is a matter of moments and 

 not of months. Thus even this experiment in its present form 

 does not convince us that a chemical exchange took place before 

 the water vapor entered the reaction, f 



*"W. Spring, Zeitschr. fur phys. Cheinie, ii, p. 536, 1888. 

 f See note on p. 406. 



