Mr. F. Guthrie on Salt Solutions and Attacked Water. 5 



There is accordingly an increase of volume when a solution 

 of salt is diluted ; and this is of course connected with the ab- 

 sorption of heat examined in § 4, Table I. When the ori- 

 ginal temperatures are restored, a mixture of strong brine and 

 water may have a volume two hundredths greater than the sum 

 of the volumes of its constituents. And when the brine con- 

 tains as little as 4 per cent, of salt, its specific gravity is sen- 

 sibly smaller than if such a proportion had been the result of 

 the mixture without contraction of the strongest brine and 

 water. 



§ 8. Refraction of Light by Brines of different strengths. — It 

 seemed, from a consideration of the numbers in Table III., that 

 at or near the point of saturation a definite hydrate of salt exists ; 

 aud that this is not merely diluted, but also actually decomposed 

 on the addition of water, so that expansion takes place. This I 

 imagined might be tested by the change in the refractive index 

 of the brine. Accordingly brines of various strengths were 

 placed in a hollow prism of 60°. The refraction was measured 

 on a goniometer (Babmet's) table provided with telescope and 

 collimator. An alcohol-flame containing sodium was employed 

 as a source of light shining through a very fine slit. The mini- 

 mum refraction being obtained, the D line was split by the spider- 

 thread. In Table IV. the empty prism is considered as giving 

 a displacement of 0°. The angular displacements are alone here 

 given, as they perfectly suffice for the detection of singular values. 



Table IV. 



Refraction of Light by Brines of various strengths. 



Temp. = 22° C. 



Per cent, of brine 

 in solution. 



Per cent, of salt 

 in solution. 



Displacement. 



! 



00 



2627 



27 45 



or 27-0125 



70 



18-39 



26 2 30 



„ 260416 



65 



1707 



25 44 



„ 25-7333 



60 



15-76 



25 32 30 



„ 25 5416 



55 



14-45 



25 20 



„ 25 3333 



50 



1313 



25 10 



„ 251666 



45 



11 82 



24 59 



„ 249833 



40 



10-51 



24 48 



„ 24-8000 



35 



919 



24 37 30 



„ 24-6250 



30 



788 



24 26 45 



„ 24-4458 



25 



657 



24 16 30 



„ 24 2750 



20 



5-25 



24 6 



„ 24-1000 







0-00 



23 23 



„ 23-3833 



These numbers show a singular value at about the 10- to 1 L 

 per- cent, solutions. 



