produced by the mutual Reaction of Solid Substances, 291 



from 58° to -5° F., and from 51° to -10° respectively. 

 Subsequently* he mixed nitrate of iron with Glauber's salt, 

 and obtained a reduction of 32° F. 



Berthelot, in his recent work on Thenno-Chemistry, devotes 

 a brief space to the subject; and the Comptes Rendus, vol. xc. 

 pp. 1163, 1282, contains a communication from Ditte calling 

 attention to this wonderful phenomenon. He considers the 

 use of concentrated acids with hydrated salts, also mixtures 

 composed solely of salts. An example is given of ammonium 

 nitrate and hydrated sodium sulphate mixed together in a 

 mortar, the loss of heat being about 20° C. 



Liquefaction of Salts. — As far as we know, when any salt 

 soluble in water is mixed with ice, liquefaction is sure to fol- 

 low, and the minimum temperature is below 0° C. But when 

 salts only are taken, the case is different. 



In some instances liquefaction is very evident, in others 

 there is none at all, and in still others it is doubtful ; while the 

 loss of heat is sometimes great, sometimes very slight, accord- 

 ing to the amount of liquefaction. Whether moistening will 

 take place or not must be decided in nearly every case by 

 actual trial; and in the preliminary experiments made with 

 reference to this point, J. have mixed the substances in a wedg- 

 wood mortar. 



From a large number of trials, the following conclusions 

 have been drawn: — 



1. As a rule, it is necessary to liquefaction that one of the 

 solid substances used should be hydrated. 



2. It is not necessary that each solid should be a salt. 

 Moistening sometimes follows the mixing of a salt with an 

 acid, a salt with a base, or a base with an acid. 



Ex. — Calcium chloride (CaCl 2 . 6 H 2 0) with tartaric acid 

 (C 4 H 6 6 ). 

 Sodium sulphate (ISTa^ S0 4 . 10 H 2 O) with potassium 



hydrate (KOH). 

 Potassium hydrate (KOH) with tartaric acid (C 4 H 6 6 ). 



3. As, in the case of liquids, metathesis will take place if a 

 compound insoluble in the menstruum can be formed, so with 

 solids, if such a compound can result, metathesis is probable 

 with liquefaction. 



4. If, by mixing two salts, an insoluble compound is pro- 

 duced, a mixture of two others like the new ones formed will 

 not, as a general thing, be attended by liquefaction. 



5. When no insoluble compound is formed, four bodies are 

 probably contained in the product, metathesis being partial ; 



* II., xxvii. p. 15. 



