CHEMICAL SCIENCE. 297 



INFLUENCE OF PRESSURE UPON THE FORMATION OF CHEMICAL 



COMPOUNDS. 



Hydrate of clilorine, which is immediately decomposed at ordinary tem- 

 peratures, and at the pressure of the atmosphere, remains for the most 

 part undecomposed, even at a summer heat, when enclosed in hermetri- 

 cally-sealed tubes, under the pressure of the clilorine which is set free 

 from a portion of it which undergoes decomposition. In such a tube, 

 when plunged into water of a temperature of 86-104 Fah., the hydrate 

 of chlorine is decomposed, but becomes partially restored on its return to 

 the ordinary temperatures. 



This decomposition is riot prevented by the exclusion of the air under 

 the pressure of chlorine gas of the tension of the atmosphere ; under 

 these circumstances, the decomposition takes place as usual at any tem- 

 perature above 32- Fah. 



A tube in which hydrate of chlorine was hermetically sealed was ex- 

 posed to the sun for a whole summer's day. It became fluid, but did not 

 indicate decomposition of the water by the setting free of oxygen. 



The author had already observed that, during the preparation of liquid 

 sulphuretted hydrogen from sulphuret of hydrogen in hermetrically- 

 pealecl tubes, colorless crystals are sometimes formed, which immediately 

 disappear on the tube being opened. 



In two tubes, in which sulphur, but no liquid sulphuretted hydrogen, 

 had separated, these crystals were found in large quantity ; they did not, 

 however, make their appearance in a third tube, in which the persulphuret 

 of hydrogen was enclosed together with concentrated muriatic acid. 

 Hence the author concludes, that the crystalline compound, which is no 

 doubt a hydrate of sulphuretted hydrogen, must be produced when a 

 small quantity of water is enclosed with hydrate free from acid ; the 

 water then combines with the sulphuretted hydrogen under the pressure 

 of the condensing sulphuretted hydrogen, (17 atmospheres.) Under this 

 pressure it is permanent at ordinary temperatures. If the tube be heated 

 in water to 86 C Fah., the compound dissolves, and rapidly becomes fluid, 

 returning to a solid state again on being cooled to the ordinary tempera- 

 t are, Prof. Wohler Ann. der Chem. und Pharm. 



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