2 Mr. F. Guthrie on Salt Solutions and Attached Water. 



of any metal having an atomic weight differing by more than 5 

 from that of sodium could be present, supposing it to be a chlo- 

 ride. On converting the chloride into a sulphate an equally 

 accordant result was got. This convinced me that I had a per- 

 fectly pure substance. 



§ 3. Preparation of the Brine. — The clearest lumps of the 

 rock-salt were washed in common and then in distilled water. 

 With these a large beaker was filled. Distilled water was poured 

 on so as to fill the beaker about two thirds. If part of the 

 salt is thus always above the surface of the brine, the latter ap- 

 pears to be saturated in twenty-four hours. After forty-eight 

 hours the brine was poured into another beaker and allowed to 

 stand until crystals began to be formed. It was then transferred 

 to a stoppered bottle and was ready for use. Although Regnault 

 and others have shown that for temperatures above 0° C. the 

 solubility of chloride of sodium in water is constant, yet the 

 precaution was taken of suspending a muslin bag containing 

 some crystals of salt from a string passing through the cork of 

 the bottle so that the crystals touched tbe surface of the brine. 

 By this means the perfect saturation of the brine was assured. 

 At 18° C. this solution contained 26*2724 per cent, of salt. 

 The solution was weighed in a long-necked flask, and was eva- 

 porated to dryness and heated to about 300° C. 



The following numbers show the results obtained by some 

 other experimenters : — 



per cent. spec. grav. 



Kopp . . Sat. at 25 C. contains 26*32 

 Kastner . „ 18*75 „ 26*72 1*2046 

 F. G. . . „ 18 „ 26-27 



F. G. . . „ 21 1*1997 



F. G. * . „ 26 1-2011 



The above specific gravities are referred to water at the same 

 temperature as the brine, as far as my own experiments are con- 

 cerned. 



§ 4. Cold produced on mixing saturated Brine with Water. — To 

 examine this point, a series of covered beaker-glasses containing 

 known weights of water, and a similar series containing satu- 

 rated brine, were placed side by side in a tin tray containing 

 water and resting on flannel. The whole arrangement was co- 

 vered with flannel and allowed to stand over night. In the 

 morning the temperature of eight or ten was found to be exactly 

 21° C. The liquids were prepared by measuring out from a 

 burette in proportions that, taking 1*1997 as the specific gravity 

 of the brine, the ratios by weight were as in columns 3 and 4 

 (Table I.). The experiments were performed by taking out a 

 water-beaker, rapidly drying its outside, pouring in the brine, 

 stirring with the thermometer, and at once reading. 



