222 PROCEEDINGS OP THE AMERICAN ACADEMY. 



The fact that this salt effloresced so readily at first prevented the 

 making of any accurate crystallographic measurements. However, it 

 was found that at a temperature of about — 5° the salt retained its 

 lustre for a sufficient length of time to afford very accurate measure- 

 ments and crystallographic study. These crystals were of a tabular 

 form, and upon looking through the plate with a polarizing micro- 

 scope no interference figure could be discerned. 



As the formula indicates, this is a hydrate of the two previous salts. 



The water of crystallization is easily lost, even at a temperature of 

 15°. The weather at this period of the investigation was extremely 

 cold, in consequence of which it was found that when the salt is kept 

 in a room with the temperature at about : — 5°, it retains its water of 

 crystallization for a period long enough to admit of weighing. The 

 salt in the form of large isolated crystals was taken from the mother 

 liquor, hastily dried between sheets of filter paper, crushed in a mortar, 

 and finally rubbed between filter papers. Then it was transferred to 

 a glass-stoppered weighing bottle, the whole operation occupying not 

 more than 80 seconds at a temperature of — 5°. From the weighing 

 bottle it was quickly removed as desired ; — the loss in weight of the 

 bottle showing the amount of salt used. The determination of the 

 water of crystallization presented several difficulties. Heating the salt 

 in an air bath at 90°-95°, it will not come to constant weight in ten 

 hours. If heated to 110°, it continues to lose in weight for a long 

 time ; in fact, there is a decomposition accompanied by the liberation 

 of chlorine. Analysis of the salt heated to 95° showed that no CI 

 had gone off, but when heated to 110° there was a marked diminution 

 of the percentage of chlorine, indicating a decomposition. At a tem- 

 perature of 104° the salt will lose weight rapidly for a while, and 

 then lose it very slowly for hours. Evidently the point where the 

 last portion of water goes off and the point where the chlorine begins 

 to be given off are nearly coincident. A great many determinations 

 were made, and by estimating the chlorine every time the point could 

 be very closely determined. Almost all the water will be given off in 

 a desiccator over sulphuric acid, but it is a long time before the last 

 trace is gone (thirty hours). 



1. In a desiccator after 30 hours, the per cent of H 2 = 8.743 



2. Heated in air bath 90-95°, at end of 4 hours = 8.476 



3. " " 140° for 1 hour = 9.874 



4. " " 105-107° for 5 hours = 10.24 



5. " " 100-105° " " = 8.765 



