VOL. LXXX.] PHILOSOPHICAL TRANSACTIONS. 6/5 



body has no share in its composition. Neither before the blow-pipe, nor in cal- 

 cination, was there any appearance of the peculiar flame, or flowers, by which 

 zinc is so strongly characterized: if any such appearance had taken place, it 

 CDuld not have escaped notice, as some of the calcinations were particularly at- 

 tended to during the process, though with a different view, the discovery of 

 sulphur or arsenic. The white matter which remains after the calcination is cer- 

 tainly not calx of zinc, for it was not acted on by spirit of salt, cold or hot, 

 while the calces of zinc are dissolved rapidly by that acid, even in the cold. 



XVllI. Report on the Best Method of Proportioning the Excise on Spirituous 

 Liquors. By Charles Blagden^ M. £)., Sec. R. S., and F. A. S. p. 321. 



In consequence of an application from government to the president. Sir Joseph 

 Banks, for the best means of ascertaining the just proportion of duty to be paid 

 by any kind of spirituous liquor that should come before the officers of excise. 

 Dr. B. was requested by that gentleman to assist in planning the proper experi- 

 ments for this purpose, and to draw up the report on them when they should be 

 finished. 



Though various indications of the strength of spirituous liquors have been de- 

 vised, applicable in a gross manner to general use, it is well known that no method 

 admits of real accuracy but that of the specific gravity. The weights of an equal 

 bulk of water and pure spirit differ from one another by at least a 6th part of the 

 weight of the former; whence it is obvious, that when those two fluids are mixed 

 together, the compound must have some intermediate specific gravity, approaching 

 nearer to that of water or pure spirit, as the former or the latter is the more pre- 

 dominant ingredient. Were it not for a certain effect attending the mixture of 

 water and spirits, which has been called their mutual penetration, the specific 

 gravity of these compositions, in a given degree of heat, would be simply in the 

 arithmetical proportion of the quantity of each of the fluids entering into them. 

 But whenever different substances, which have a strong tendency to unite toge- 

 ther, are mixed, the resulting compound is found to occupy less space than the 

 substances forming it held in their separate state; therefore the specific gravity of 

 such compounds is always greater than would be given by a simple calculation 

 from the volume of their ingredients. Though it be a general fact, that such a 

 decrease of bulk takes place on the mixture of substances which have a chemical 

 attraction for each other, yet the quantity of this diminution is diff'erent in them 

 all, and, under our present ignorance of the intimate composition of bodies, can 

 be determined by experiment only. To ascertain therefore the quantity and law 

 of the condensation, resulting from this mutual penetration of water and spirit, 

 was the first object to which the following experiments were directed. 



All bodies in general expand by heat ; but the quantity of this expansion, as 



4R2 



