6/6 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 QO. 



well as the law of its progression, are probably not the same in any 2 substances. 

 In water and spirit they are remarkably different. The whole expansion of pure 

 spirit from 30° to 100° of Fahrenheit's thermometer, is not less than -^^th of 

 its whole bulk at 30°; whereas that of water, in the same interval, is only , \ yth 

 of its bulk. The laws of their expansion are still more different than the quanti- 

 ties. If the expansion of quicksilver be, as usual, taken for the standard, the 

 expansion of spirit is indeed progressively increasing with respect to that standard, 

 but not much so within the above-mentioned interval; while water kept from 

 freezing to 30°, which may easily be done, will absolutely contract as it is heated 

 for 10° or more, that is, to 40° or 42° of the thermometer, and will then begin 

 to expand as its heat is augmented, at first slowly, and afterwards gradually more 

 rapidly, so as to observe on the whole a very increasing progression. Now mix- 

 tures of these 2 substances will, as may be supposed, approach to the less or the 

 greater of those progressions, according as they are compounded of more spirit 

 or more water, while their total expansion will be greater, according as more 

 spirit enters into their composition; but the exact quantity of the expansion, as 

 well as law of the progression, in all of them, can be determined only by trials. 

 These were therefore the 2 other principal objects to be ascertained by experiment. 



The first step towards a right performance of the experiments, was to procure 

 the two substances, with which they were to be made, as pure as possible. Dis- 

 tilled water is in all cases so nearly alike, that no difficulty occurred with regard 

 to it; but the specific gravity of pure spirit, or alcohol, has been given so very 

 differently by the authors who have treated of it, that a particular set of experi- 

 ments appeared necessary for determining to what degree of strength rectified 

 spirits could conveniently be brought. The person engaged to make these ex- 

 periments was Dr. Dollfuss, an ingenious Swiss gentleman then in London, who 

 had distinguished himself by several publications on chemical subjects. Dr. Doll- 

 fuss, having been furnished by government with spirit for the purpose, rectified 

 it by repeated and slow distillations, till its specific gravity became stationary in 

 this manner of operating: he then added dry caustic alkali to it, let it stand for 

 a few days, poured off the liquor, and distilled it with a small addition of burnt 

 alum, placing the receiver in ice. By this method he obtained a spirit whose 

 specific gravity was .8188 at 6o°of heat. Perceiving however that he could not 

 conveniently get the quantity of spirit he wanted lighter than .82527 at 6o°, he 

 fixed on that strength as a standard, to which he found the above-mentioned 

 lighter spirit could be reduced by adding to it a , g ^ „ th part of water; and with 

 this spirit and distilled water he made a series of experiments for determining the 

 specific gravity of different mixtures of these fluids in different degrees of heat. 



The process followed by Dr. Dollfus is not here given as the best possible for 

 obtaining pure spirit; nor was the result of it in fact the lightest alcohol that has 

 been procured. Some spirit has been tried since that time, whose specific gravity 



