28 J. Y. Buchanan — Specific Gravity of Soluble Salts 



bottle, while the crystals were collected, allowed to drain, and 

 dried, in the ordinary way. The temperature which the mix- 

 ture had when separated is noted as that at which the crystals 

 and the mother-liquor were in equilibrium ; and it is exactly 

 at this temperature that they have to be brought together 

 again in order to determine the specific gravity of the salt. 

 It is at this temperature also that the specific gravity bottle is 

 weighed when filled with distilled water and with mother- 

 liquor respectively. In fact the temperature of equilibrium 

 and of separation is the only temperature used. 



In Table I, the experimental details are given in full in the 

 case of one salt, namely, caesium chloride. For the other salts 

 the results only are given, and they are collected in Table II. 



All the weights given in this paper represent the weight 

 in vacuo. 



The specific gravity bottle which was used was one of the 

 common and convenient form which has a thermometer for a 

 stopper and a lateral capillary tube for the adjustment of level. 

 Its nominal capacity was fifty cubic centimeters. On three 

 occasions one of 25 cc capacity was used for determining the 

 displacement of the mother-liquor. 



The concentration (m) of the mother-liquor is determined by 

 titration with tenth-normal silver nitrate solution. This solu- 

 tion was made with the greatest care and contained exactly 17 

 grams of silver nitrate in one liter, at the ordinary temperature 

 of the laboratory at the time. The burette used was divided 

 into tenths of a cubic centimeter and had a capacity of 50 cc . 

 The determination of the halogen was not made until the 

 specific gravity had been determined, and, if the concentra- 

 tion was not already known within narrow limits, a prelimin- 

 ary titration was made, after which the volume of mother- 

 liquor was weighed, which would certainly require 10d=l cc for 

 titration. The capacity of the burette from to 40°° was 

 determined by weight with great care. The concentration is 

 stated in gram-molecules salt per 1000 grams of water. 



For weighing out the salt and passing it directly into the 

 specific gravity bottle a special and convenient form of weigh- 

 ing tube was used. It was made out of a stoppered specimen 

 tube with an internal diameter of 2 centimeters and a length 

 of 7 or 8 centimeters. The lower end of this tube was opened 

 and a piece of thin glass tube joined to it before the blowpipe. 

 This tube, which had a length of about 3 centimeters, had an 

 external diameter such that it could just pass freely through 

 the neck of the specific gravity bottle. The wide end was 

 closed with a glass stopper and the narrow end with a small 

 india rubber cork. 



It was the custom to work so as to have about 15 cc of dry 



