CHEMICAL SCIENCE. 197 



COLORATION OF GLASS. 



M. Pelouze having observed that the glasses of commerce were 

 colored yellow by carbon, sulphur, silica, boron, phosphorus, 

 aluminium, and even by hydrogen, was led to make a series of ex- 

 periments for ascertaining the cause of the identity of the results 

 with such different reagents. His conclusions, verified beyond a 

 doubt, have a considerable importance in reference to the possible 

 perfection of glass manufacture. His first conclusion is, that " all 

 the glasses of commerce contain sulphates." These salts (sul- 

 phates of soda, potassa, or lime) render the glass more or less 

 alterable by atmospheric agency, and come into the glass from 

 two soui-ces, either directly from the use of these sulphates as a 

 flux, or from the presence of the sulphate of soda as an impurity 

 in the commercial carbonate. The effect of their existence may 

 be seen by examining many of the panes of glass in om* windows, 

 which have been for some years exposed to the air, when the sur- 

 face of the glass will be found to be corroded and pai'tially opaque 

 like ground glass, and by examination under a magnifier will be 

 found to be covered with crystals. lie found these sulphates 

 present from one to three per cent, in all the commercial glasses, 

 window, plate, table, bottle, and Bohemian glass ; he also found 

 two jier cent, of sulphate of soda in a glass from Pompeii. The 

 coloration is now easily explained; the reagents named above 

 reduce the sulphates and produce an alkaline sulphuret, which has 

 the property of giving the yellow color. He jjroved this by show- 

 ing, first, that when the glass materials were carefully ijurified 

 from sulphates, no color was produced by carbon, hydrogen, bo- 

 ron, silicon, phosphorus, or aluminium ; and, secondly, that an 

 alkaline sulphuret added to the pure materials produced the color. 

 — Acad, des Sciences, Paris, 1865. 



CHEMICAL CONSTITUTION OF THE BRAIN. 



Liebreich has discovered in the fresh brain of man and animals 

 a crystalline substance which he has called protagon. After free- 

 ing it from blood and membranes, the brain should be rubbed in a 

 mortar to a fine j^aste, and the mass agitated in a flask with water 

 and ether. Cholesterine and soluble substances being thus re- 

 moved, after filtering, the mass is treated with 85 per cent, alcohol 

 at 45° C. in a water bath, and then filtered through a water-bath 

 filter. The filtrate being cooled to 0° C, an abundant flocculent 

 l^recipitate falls, which must be filtered and washed with cold 

 ether to free it from cholesterine ; the mass being then dried un- 

 der an air-23ump over snlj)huric acid, moistened with a little water 

 and dissolved in alcohol at 45° C, the solution, after filtration, is 

 to be cooled gradually upon a water bath to the mean tempera- 

 ture of the air, when it will be found filled with microscopic crys- 

 tals, — these differ somewhat in form according to the quantity of 

 alcohol used. The pure protagon thus obtained was found to have 

 the formula C232 H241 N4 PO44. Dried, it is a light flocculent pow- 

 der, soluble in hot alcohol and ether, but with difficulty in cold. 

 17* 



