Remarltahk Chunges of Jj^nily iy Cold. gi 



ItiiowkJge wliatevcr may be its nature ; we may afterwards choofe the good, and reje£l the 

 ufelefs. (Qu.?) 



Theory is the General ; Pra<5lice is the Army. 



Experiment is the interpreter of the contrivances of nature. This interpreter never 

 deceives us. Our judgment fomeiimes mifleads itfclf in expectation of confequences 

 which experiment rcfufes to verify.— We mud recur to experiment, and vary the circum- 

 flanees until we have deduced general rules, for it is experience which afFords the true 

 rules. — But you may afk, What is the advantage of thefe rules ? I reply, that they direct 

 our refearches into nature, and the operations of art. They prevent us from deceiving our- 

 felves or others by the promife of refults which cannot be obtained. 



There is no certainty in fciences to which fome part of the mathematics cannot be ap- 

 plied, or which do not depend in fome manner upon mathematical knowledge. 



In the ftudy of fciences which depend on the mathematics, thofe who do not confult 

 nature, but authors, are not the children of nature. I would call them her grand-children. 

 Nature, in fa£t, is the fole leader of true genius. But fuch is the folly of men. He who 

 choofes rather to learn from the original fource, inftead of applying to authors^ becomes 

 an obje£l of derlfion for his fingularity *. 



Obfevvatlons and Experiments on the Formation of Sulphate of Soda, or Glauler's Salt, in Salt 

 WaterSy at a Temperature beneath the Freezing Point of Water, and upon' an eafy Method of 

 difengaging all the deliquefcent Salts. By M. Gren \. 



H E influence of temperature upon the eftabliflied laws of mutual decompofition of 

 the neutral and middle falts, is a circumftance very eflential to be obferved. Many falts 

 are not decompofed above the temperature of freezing water, though very well beneath 

 that temperature. Such, for example, are the fulphate of alumine and the muriate of 

 foda; the fulphate of magnefia and the fame muriate. 



The formation of Glauber's fait during congelation in fait water, wherein previous ana- 

 lyGs did not difcover it, had long fince engaged the attention of the author. He concluded 

 that the fulphate of foda owed its origin to the mutual decompofition of fulphate of lime 

 and muriate of foda, at a temperature below zero. A more accurate analyfis of thefe wa- 

 ters after the fevere cold of 1794 and 1795, proved that he was miftaken, and that the 

 fulphate of foda had been formed by the double decompofition of the muriate of foda and 

 the fulphate of magnefia. The excefllve cold of 1785 had already exhibited this decom- 

 pofition to Scheele, and he had (hown that fulphate of foda was produced from a mixture 

 . of two parts of the folution of fulphate of magnefia, and one part of the muriate of foda, 

 erpofed to the temperature of ice. 



* Profeffor "Venturi intends to publifh as fpeedily as circumftances will permit, Ip three complete treatifes, the 

 whole works of De Vinci on mechanics, hydraulics, and optics. N. . . . ■ 



-. f The memoir of M. Gren was addreffed by himfelf in thanufcript to the Council of Mines in Fraricl, 

 ivhc publiflied it in the xxviith Number of the Journal des Mines. Citizen Defcotiis abridged the fame in the 

 s^ivth volume of the Annales de Chimie, pageiu. The above pspsr is a tranfiation frpm his. abridgment. N. 



N2 M. Grca 



