1872.] 



Solutions of Glauber's Salt. 



Ill 



with my experience. Not much more than half an ounce of a compara- 

 tively weak solution of Glauber's salt, such as 1 salt to 1 water, may rise 

 from 20° to 5fi° on suddenly becoming solid ; and with 2 or 3 salt to 1 of 

 water the rise may not be greater, especially if a considerable mass of the 

 two abnormal hydrates be already formed, and only a small portion of the 

 solution remain to become solid. 



In another experiment, 3 parts salt to 1 of water were boiled and fil- 

 tered into two test-tubes and one 2-ounce flask. One tube, on being put 

 into the freezing-mixture, sank to 35°, when the solution suddenly became 

 solid, and the thermometer rose to 78°. The other tube-solution threw 

 down so large a quantity of anhydrous crystals as to prevent the reading 

 of the thermometer. The solution in the flask threw down anhydrous 

 crystals at 44°, and then sank very slowly to 40°, where it remained sta- 

 tionary upwards of ten minutes, in consequence of the liberation of heat- 

 currents, occasionally rising to 41°. A large quantity of transparent 

 crystals was now heaped up on the bulb of the thermometer ; the tempe- 

 rature descended to 38°, with slight starts upwards ; and in slowly de- 

 scending to 33°, there was a large increase of the transparent crystals. At 

 32° the flask was transferred to a fresh freezing-mixture at 10°, and the 

 solution slowly descended to 22°, when it was again removed to a fresh 

 freezing-mixture, also at 10°. Soon a number of large fern-like crystals 

 covered the side of the flask, starting, apparently, from the top of the co- 

 pious deposit first produced, and rendering the upper part opaque in a 

 well-defined line. The temperature rose to 26°, and continued there 

 gome minutes, when the solution suddenly crystallized, and the thermo- 

 meter rose to 48°. 



Supersaturated solutions of potash alum, exposed to low temperatures, 

 behave much in the same way as the solutions of double salts described in my 

 former paper. A solution of 300 grains of the salt in 1^ oz. of water, boiled 

 and filtered into clean test-tubes, and, when cold, put into a freezing-mixture 

 at about 0° F., displays the beautiful ivy-leaf kind of foliage, of a brilliant 

 white colour, already referred to. The growth starts from the bottom or 

 from the surface of the solution, or from both, and soon the whole solution 

 becomes solid. If the tube be put into water at 32°, the solid rapidly 

 melts, and the liquid is a clear bright supersaturated solution as before. 



Lowel, in his first memoir (An. de Ch. et de Ph. 3 serie, tome xxix.), 

 found that when supersaturated solutions of Glauber's salt, in sealed tubes, 

 were subjected to temperatures varying from —8° to — 10° C, they often 

 froze and burst the tubes. In one case, where the tube did not burst, the 

 solution, in thawing, caused the state of supersaturation to cease. In another 

 case the frozen solution thawed, and the liquor became supersaturated as 

 before. Lowel could not reproduce this last effect, nor explain why the 

 thawing should lead to the formation of the ten-atom salt. But as he did 

 not know the conditions of clean and unclean, he was constantly looking 

 out for some catalytic action in the sides of his vessels to explain the many 



