RegnaulVs Researches upon the Dilatation of Gases. 63 



quantity of the resin before mentioned (soluble in ether) is form- 

 ed ; this though is capable of being converted into the acid, by 

 the action of potash, a high temperature, and free access of air. 

 Thus then it will be seen, that the action of potash, instead of 

 being a means of showing that spermaceti and cholesterine are 

 two substances of entirely different natures, affords strong evi- 

 dence of their being similar bodies. Further, the action of potash 

 upon spermaceti, is to produce athalic acid and athal, the former 

 capable of forming soaps with the alkalies, and the latter of being 

 converted into the former by an alkali and a high temperature. 



The action upon cholesterine is to form an acid (which it is 

 impossible for me as yet to name) and a basic resin ; the former 

 forms soaps with alkalies, and the latter by the action of potash 

 at a high temperature is converted into the former. 



This article is meant as an appendix to the one on spermaceti, 

 and as an additional proof of the analogy that exists between 

 that body and cholesterine, they being two of a class of bodies 

 which will no doubt be found to be tolerably numerous, and 

 which class I propose to call pseiido gras. Among them may be 

 mentioned spermaceti, cholesterine, athal, ambreine, and proba- 

 bly stearerine and elaierine, two fatty substances found in linseed 

 oil, and which M. Chevreul brought to the notice of the Acade- 

 my of Sciences not long since. This class of bodies would ap- 

 pear to be a link between the fats and resins. 



Paris, July 8, 1842. 



Art. IX. — A Review of the Researches upon the Dilatation of 

 Gases, by M. V. Regnault ; by J. Lawrence Smith, M. D. 



On the dilatation of atmospheric air. — " There does not exist 

 in physics a numerical element that has been submitted to so 

 many experimental determinations, as the coefficient of the dila- 

 tation of air ; and nevertheless we cannot say that this coefficient 

 has been determined with sufficient precision. 



" The beautiful experiments of Gay Lussac upon the dilatation 

 of gases, seemed to have completely decided this question. He 

 showed by a great number of experiments that the coefficient of 

 dilatation between 0° and 100° Cent, was the same for all gases 

 and vapors, when they are not extremely near their point of con- 



