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422 Scientific Intelligence 



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SCIENTIFIC INTELLIGENCE* 



L CHEMISTRY AND PHYSICS. 



1, On the calculation of the densities of vapors. — Kopp has suggested 

 a mode of calculating the deuvsitles of vapors "when referred to air as 

 unity, "vvhicli is shorter and more convenient than the ordinary process. 

 If the equivalent of a body he referred to oxygen taken as 8, and its 

 vapor-density to air as 1, we find that the quotient of the atomic weight 

 by the density is equal to one of the following numbers, 



28-88 14-44 7-22 



The number 28'88 corresponding to a condensation of four, 14*44 to 

 one of two, and 7-22 to one of one volume. The author calls these 

 numbers normal quotients. When the density of the vapor of a sub- 

 stance has been determined approximately by experiment, the quotient of 

 its equivalent by this density is a number which is very near one of the 

 preceding. This operation shows at once the mode of condensation of 

 the vapor. Conversely, it is always easy to calculate the vapor density by 

 dividuig the equivalent by one or the other of the normal quotients. 

 Thus, for a great majority, if not for all organic compounds, the divisor is 

 28*88, because the substances correspond to 4 vols. Thus in the case of 

 acetic ether we have for the equivalent SS and for the experimental den- 



sity 3'112, now ^7:-^- ^28'2, a result which indicates a condensation into' 



go 



4 vols. The theoretic density is therefore- r=:3'047. ' » 



28*88 * 



This mode of calculating the vapor-density of a body does not require 

 a knowledge of the densities of the vapors of the elements contained in 

 the body. It is only necessary to know the equivalent of the body itself. 

 It follows that bodies which have the same equivalent will usu.^Ily ha\^e 

 the same density of vapor. Thus phenol, CiaHeOa, and bisulphid of 

 methyl, C4H6S4, have the same equivalent, 94, and the same density, 

 3'255. When the densities of bodies having the same equivalent are 

 not the same they will of course be connected by simple ratios. — Comptes 

 Rendus, xliv, 1347. 



\NQtc. — If we take the density as well as the equivalent and combin- 

 ing volume of hydrogen =1, the vapor-densities of all other gases and 

 vapors are either equal to their equivalents or to their equivalents divided 

 by a low number. In general terms, with these units, the vapor-densities 

 are equal to the equivalents divided by the combining volumes. Thus 

 the densities of nitrogen, chlorine, iodine, bromine, &c., are simply repre- 

 sented by their equivalents 14, 35'5, 127, 80. The vapor-deusity of sul- 



phur is —— 48, that of oxygen -=16. It must be remembered that 



upon this system 2 vols, correspond to 4 vols, upon the scale in which the 

 density of air =1. Ilei.^0 the vapor-densities of nearly all organic 

 compounds are simply half their equivalents, when all the hydrogen con- 

 stants are taken as units. If it be objected to this system that experi- 

 ment always compares the weights of equal volumes of air and vapor, it 



