and Attached Water 



359 



tions, previously saturated at 12° C, for three hours at 0°, and 

 determined the strengths by evaporation &c, in some cases by 

 determination of one constituent by the usual chemical means. 

 I find these latter determinations agree very closely with those 

 of Kremers throughout. Indeed, as will be seen, we seldom 

 differ more than 03 per cent. For the determination of the 

 temperatures above 0° C. at which salts and their hydrates 

 separate, I have found, contrary to my anticipations, the more 

 exact method to be in most cases to warm a given weight of 

 the salt with its proper percentage of water in a stoppered 

 bottle till solution was effected, and then by repeated observa- 

 tion find the temperature of incipient crystallization, rather 

 than attempt to keep the water and salt for a length of time at 

 a constant temperature and then determine the strength. The 

 latter method, however, is of course especially available for 0° 

 and 100° C. 



§ 127. Separation of Ice, of Subcryohydrate and of NaCl 

 from solutions of that salt. — The following Table (XVI.) 

 shows the temperature below 0° C. at which ice begins to be 

 separated from solutions of common salt of different strengths. 

 In selecting these strengths I have chosen several close to the 

 critical points, namely to that of distilled water, to that of the 

 cryohydrate, and to that of saturation. And in the case of 

 other salts I have, as far as possible, examined solutions of the 

 same percentage- weight strengths. The ascent (see fig. 1. 

 NaCl) is so steep from the cryohydrate to 0° C. that I have 

 only been able to introduce one observation. As my deter- 

 mination for 0° C. was 26*27 (§ 11), and Poggiale's was 26*28, 

 I have no hesitation in adopting Poggiale's for + 25° and + 40°. 



Table XVI. 



NaCl 



H 2 



Temperature 





per cent, by 

 weight. 



per cent, by 

 weight. 



Centigrade at 



which a solid 



is formed. 



Nature of solid. 



1 



99 



-83 



Ice. 



2 



98 



- 0-9 



fi 



3 



97 



- 1-5 



>» 



.4 



96 



- 2 2 





7 



93 



- 4 2 



>> 



10 



90 



- 6-6 



» 



13 



87 



- 91 



>> 



15 



85 



-110 





16 



84 



-119 



' 



19 



81 



-15-5 



If 



20 



80 



-170 





22 



78 



-20 



>f 



23-6 



76-4 



-220 



Cryohydrate. 



25 



75 



-1201 



o-o ; 



f Subcryohydrate. 



26-27 



7373 



\ NaCl. 



26-5 



73-5 



+250 



„ (Poggiale). 



26-8 



73-2 



+ 400 



» ( p °gg iale )- 



