and Attached Water. 275 



arises from the circumstance that the cryohydrate is soluble both 

 in water and alcohol, and that ice is soluble in the liquid cryo- 

 hydrate. We are here reminded of the phenomenon of the maxi- 

 mum density of water, which I have already endeavoured to 

 connect with the formation of a cryohydrate of water (in § 36) . 

 § 100. For some reasons this melted cryohydrate of alcohol, 

 or spirit of wine containing 60*93 water and 39*07 of alcohol, 

 should be the standard or proof spirit in all alcoholometry. 

 English proof spirit contains 50'5 per cent, by weight of alcohol. 

 It accordingly should begin to solidify at — 38° (about the free- 

 zing-point of mercury). At lower temperatures it becomes a 

 pasty mass, but never perfectly brittle, on account of the un- 

 freezable alcohol in excess above that of the cryohydrate. Spirits 

 of 39 per cent, and under become perfectly solid before the 

 temperature reaches —36°. The very fact that weaker spirits 

 wholly solidify while stronger never do so is, I conceive, a com- 

 plete proof of the existence of a cryohydrate. For if under all 

 circumstances water alone solidified, alcohol would be left even 

 from the weakest spirits, and total solidity could never be reached. 

 § 101 . The above considerations, of course, only apply to the 

 chemically pure substances alcohol and water ; how far the sugar, 

 caramel, fusel, essences &c. of commercial spirits, and the innu- 

 merable substances in wines and beers may affect the solidifica- 

 tion is a matter for future research. It is quite possible, for 

 instance, that in some rums the 10 per cent, alcohol above that 

 required for the cryohydrate might find sufficient foreign matter 

 present to form therewith a solid, and so allow the whole to 

 solidify. 



§ 102. I believe that the detection of this 4-molecule hydrate 

 of alcohol reconciles the apparently contradictory results of 

 former experimenters. Thus, looking on wine as a 10-per-cent. 

 spirit of wine, M. Melsens obtained by a freezing-mixture 40 

 per cent, of ice. I judge from Table XI. that the temperature 

 reached was — 8°, if we make no allowance for loss of ice during 

 manipulation. 



§ 103. The evidence adduced by Messrs. Dupre, Page, and 

 others points to the existence of at least one hydrate of alcohol ; 

 but I am not prepared to say that such hydrate is necessarily 

 identical with the 4-molecule cryohydrate which we have been 

 considering. It must be remembered in this connexion that the 

 cryohydrates of solid salts contain more water than any other 

 known hydrate ; and the existence of the 4-molecule cryohydrate 

 rather, I conceive, tends to show that the ordinary hydrate 

 of alcohol contains less water, and is, as some of Dupre and 

 others' experiments may be interpreted as showing, the 3-bydrate 

 C 2 H 6 + 3H 2 0. 



