274 Frederick Guthrie on Salt Solutions 



separated is in all cases ice. This, however, is not the case. Down 

 to the ratio 65 water and 35 alcohol, the ice spicula freely mo- 

 ving in the mother-liquid are easily recognized. If they are 

 remelted they invariably reform at the same temperature. At 

 ratios of 60 water to 40 alcohol and stronger, the aspect of the 

 solid formed is quite different. The liquid may then acquire 

 the consistency of Canada balsam, and yet, if kept still, it may 

 remain perfectly transparent. On rubbing with the thermometer- 

 bulb or with a glass rod minute crystals are formed, the liquid 

 becomes more mobile, resembling old honey. It offers a notable 

 case of a condition of supersaturation producing a temporary 

 colloid condition. 



§ 98. Finding that this phenomenon was first noticeable at 

 about the solution of the ratio 60 water to 40 alcohol, and reflect- 

 ing that this is nearly the ratio of one molecule of alcohol to four 

 of water, I made a spirit of exactly this molecular ratio, namely 

 39*07 alcohol and 60*93 of water by weight. On submitting this 

 to the action of a cryogen, I found the remarkable result that 

 nothing separated till the temperature — 34° was reached, although 

 both weaker and stronger solutions begin to solidify at higher 

 temperatures. The solid formed in this case is perfectly white 

 and opaque, and the temperature remains constant till the whole 

 has become perfectly dry. This pearly aspect and the constancy 

 of temperature throughout the solidification betray the cryohy- 

 drate. Both weaker and stronger spirits sink in temperature as 

 they solidify — the former until by the elimination of ice it pre- 

 sents a mother-liquor of the 4-hydrate composition, the latter by 

 the elimination of liquid alcohol as the solid 4-hydrate is formed. 



§ 99. When, therefore, a dilute alcohol (say 95 water to 5 

 alcohol) is cooled, ice separates out, the spirit becomes stronger 

 and stronger, and the temperature lower and lower. When the 

 ratio C 2 H 6 + 4H 2 is reached the temperature —34° C. is 

 reached, and the remainder of the solution is a cryohydrate of 

 alcohol whose melting- and freezing-point is —34°, and whose 

 composition is C 2 H 6 Q + 4H 2 0. 



On the other hand, if a spirit alittle stronger than C 2 H 6 + 4 H 2 

 is subjected to cold, nothing separates till about —27° C. At 

 this temperature the cryohydrate C 2 H 6 0-J-4H 2 begins to 

 separate out, and as it relinquishes the alcohol the solidifying- 

 point of the mother-liquor falls. Observe, the cryohydrate sepa- 

 rates from alcohol at a temperature above its own meltiug-point 

 when alone. It follows from this that solidification may com- 

 mence at the same temperature in two spirits of different strengths, 

 provided they are both close about the 4-molecule hydrate in 

 composition. But while in the weaker the solid will be ice, in 

 the stronger it will be the cryohydrate. The apparent anomaly 



