Intelligence and Miscellaneous Articles. 



229 



lowing Table has been drawn up, in which the resistances are ex- 

 pressed in Siemens's units — that is, compared to a column of mercury 

 at zero, 1 metre in length and having a section of 1 square metre : — 



Density at 

 18°-5. 



Volume of SO*H 

 per cent. 



Resistance at 22°, 

 Hg = l. 



Diminution for 1°. 



0-9985 



00 



744807 



0-47 per 100 



1-0000 



0-2 



464170 



0-47 



1-0504 



8-3 



34461 



0-65 



> 



1-0989 



142 



18909 



0-65 



f 



1-1431 



20-2 



14961 



0-80 



j 



1-2045 



28-0 



13107 



1-32 



i 



1-2631 



35-2 



13106 



1-26 



7 



1-3163 



41-5 



14258 



1-41 



J 



1-3597 



460 



15731 



1-57 



J 



1-3994 



50-4 



17691 



1-58 



1 



1-4482 



55-2 



20755 



1-42 



, 



1-5026 



60-3 



25523 



1-79 



> 



1-8380 



1000 



78742 



2-66 



» 



The resistances in the above Table have been corrected by a dimi- 

 nution of 0*2 per cent., in accordance with a note, at the end of the 

 memoir. They can be represented by a very regular curve, which has 

 a minimum ordinate when the density of the solution is 1-233. Hence 

 acidulated water which contains 31*6 per cent, of monohydrated 

 acid offers the least resistance to the passage of the current. The 

 coefficient of reduction with the temperature is supposed constant, 

 although this constancy has only been demonstrated directly for so- 

 lutions of sulphate of zinc ; hence this coefficient must not be ap- 

 plied to great variations of temperature. — Poggendorff's Annalen, 

 vol. cxxxviii. ; Annates de Chimie et de Physique, April 1870. 



ON LIQUIDS OF HIGH DISPERSIVE POWER. BY WOLCOTT GIBBS, 

 M.D., RUMFORD PROFESSOR IN HARVARD UNIVERSITY. 



Of the liquids which have hitherto been proposed for the construc- 

 tion of prisms, bisulphide of carbon unquestionably presents the 

 greatest advantages. It is cheap, colourless, and unites a moderately 

 high mean refractive to a very high dispersive power. By tacit con- 

 sent a prism of 60° filled with this liquid has come to be adopted as 

 a sort of standard. The disadvantages of the bisulphide are equally 

 well known ; and I have spent no little time and labour in the en- 

 deavour to find a liquid with a still higher dispersive power, less 

 volatile, less sensitive optically to changes of temperature, and less 

 offensive in odour. In these efforts I have not been altogether suc- 

 cessful, no one liquid examined possessing all the qualities desired. 

 Many organic liquids with high dispersive powers are difficult to 

 prepare in a state of purity, and speedily become discoloured by 

 absorption of oxygen from the air. Such are oil of cassia, the colour- 

 less oil obtainable from balsam of Peru, and others. The thallic al- 



