146 



SCIENCE. 



[N. K. Vo). XV. No. 869. 



a diagram illustrating the solubility curves 

 for the system NaCl— Na.SO,— H,0 at 10°, 

 21.5°, 25°, 27°, 30°, 33° and 35°. It was 

 shown that at temperatures above 33° the 

 curves represented equilibrium conditions be- 

 tween sodium chloride and anhydrous sodium 

 sulphate, and no abnormalities presented 

 themselves. Between 33° and 17°, however, it 

 was found that in solutions containing but 

 small amounts of sodium chloride and in con- 

 tact with solid sodium sulphate, the equilib- 

 rium conditions were determined by the 

 solid salt being in the form of the decahy- 

 drate, and the solubility curves for this dec- 

 ahydrate are very much flatter than the cor- 

 responding curves for the anhydrous salt. 

 But as the amount of sodium chloride in the 

 solution increased, at temperatures between 

 33° and 17°, there was always a sudden 

 change in the direction of the solubility curve 

 for sodium sulphate, which was found to be 

 caused by the sodium sulphate present as 

 solid phase, having gone over to the anhy- 

 drous form. In order to check this view, the 

 experiment was made of placing large well- 

 formed crystals of sodium sulphate decahy- 

 drate in two test-tubes, one containing a 

 saturated solution of sodium sulphate alone, 

 and the other a solution nearly saturated with 

 sodium chloride, as well as sodium sulphate. 

 Both test-tubes were fitted with, cork stoppers 

 carrying thermometers. They were then im- 

 mersed in a water-bath and the temperature 

 gradually raised. At 28° the crystals in the so- 

 dium chloride solution gradually became opal- 

 escent around the edges, then rather rapidly be- 

 came entirely opaque and showed a tendency 

 to fall apart in a loose powder. The material 

 had undoubtedly gone over to the anhydrous 

 salt, although the crystals which were in the 

 tube containing only water and sodium sul- 

 phate showed no change until the tempera- 

 ture reached 33°. It thus appeared that the 

 transition temperature for the change of 

 sodium sulphate decahydrate to anhydrous 

 salt had been displaced by the presence of 

 sodium chloride. This was regarded as of 

 considerable significance, and is important in 

 connection with the suggestions on this sub- 

 ject in the study of the change of gypsum to 



calcium sulphate hemihydrate, made by Van't 

 Hoff and Armstrong, Vater and Cameron. 



The solubility curves for sodium sulphate 

 heptahydrate in solutions of sodium chloride 

 were shown to be very similar to those for the 

 decahydrate. In the case of the decahydrate at 

 lower temperatures and the heptahydrate, the 

 curves were shown to have minimum points, 

 the significance of which is not apparent at 

 the present time. 



'The Evolution of Metallic Retorts' (with 

 samples) : W. H. Seaman. 



Before commencing the paper the speaker 

 showed a very perfect copy, just received 

 from England, of Boerhaave's ' New Method of 

 Chemistry,' in two volumes, second edition, 

 1741. Boerhaave was born in 1668, died in 

 1738, was famous as a physician, botanist and 

 chemist, and was one of the first to recognize 

 the independence of the latter science. 



The first metallic retorts were copper flasks 

 just like the olive-oil flasks of the early chem- 

 ists with a gallows screw added. In a lot of 

 scrap of Professor Henry's apparatus about to 

 be sold thirty years ago, the author found two 

 wrought-iron retorts with walls a centimeter 

 thick, and shaped just like a glass tubular re- 

 tort that are types of this class. 



The next retort exhibited was a pear-shaped 

 vessel. It had a feed wheel on top, and was 

 set in an egg stove, the bottom made red hot 

 and KClOj fed in by the wheel. The was 

 taken off by the side pipe. 



Next was a kettle-shaped retort patented by 

 the author. Its peculiarity is that all parts 

 draw together by the gallows screw, while the 

 top is diu'able with ground joint, and the bot- 

 tom, being thin, heats quickly and can be 

 cheaply renewed. 



Next we have the cylindrical sheet metal re- 

 tort which admits of moving the bunsen 

 burner along its length so as to decompose the 

 charge in successive portions. 



The latest development is the little frus- 

 trum of a cone, with gallows screw top and 

 two pipes, one for delivery and one for the 

 introduction of an inert gas or other purpose 

 that may be desired. In this oxygen may be 

 made, coal distilled, etc. They are sold by the 

 Chicago Laboratory Supply Co., price one 



