Chemistry and Physics. 397 



horizontal manometer. Each division of the upper portion of the 

 scale tube corresponds to 1/10000 of the volume of this measuring 

 pipette, each division of the lower portion to 1/1000 of this vol- 

 ume. The measurement is effected by adjusting the level of the 

 mercury till the manometer index stands at zero and then reading 

 off the volume on the scale. The second operation consists in 

 transferring the air thus measured to an Orsat tube containing . 

 potassium hydrate and allowing it to remain one or two minutes 

 to effect the absorption of the carbon dioxide. The third opera- 

 tion consists in returning it to the measuring pipette, adjusting 

 the mercury to the manometric zero, and reading off the diminu- 

 tion of volume on the scale tube. For air containing up to 0*4 

 per cent of CO„ the finer tube is employed ; but for air more im- 

 pure than this, the lower and larger scale tube is used. The 

 results of measurements made with this apparatus compared with 

 those given by Sonden's larger apparatus and by Pettenkofer's 

 method are entirely satisfactory. — Ber. Berl. Chem. Ges., xx, 

 2129, July, 1887. G. E. b. 



5. On the Atomic Weight of Silicon. — The atomic weight of 

 silicon which is usually employed rests upon two not very accord- 

 ant determinations of the ratio of silicon tetrachloride to silver 

 made by Dumas. Thorpe and Young have undertaken a new 

 determination of this important constant, based on an estimation 

 of the ratio of silicon tetrabromide to the silicon dioxide formed 

 on treating the tetrabromide with water. The tetrabromide was 

 prepared by passing bromine vapor over a strongly heated mix- 

 ture of pure silica and finely ground willow charcoal such as is 

 used in the manufacture of gunpowder. The rectified product 

 was shaken with mercury, decanted, placed in contact with cop- 

 per for some weeks and distilled in a current of dry nitrogen. It 

 was absolutely clear and colorless and boiled constantly at 153°. 

 Bulbs were filled with the tetrabromide without exposure to air, 

 by the same method which was used by Thorpe for titanium. A 

 bulb, containing a weighed quantity of the bromide, was placed 

 in a well stoppered bottle with 10 times its weight of water, and 

 broken by shaking. The turbid liquid was decanted into a tared 

 crucible and evaporated over a water bath, an equal volume of 

 water being evaporated under the same conditions in the tare. 

 The two crucibles were dried in an air bath at 160°, then ignited 

 in a muffle, allowed to cool and weighed by the method of vibra- 

 tion, employing all the necessary precautions. Nine separate de- 

 terminations were made, giving values ranging from 28*243 to 

 28*429 as the atomic weight desired. The mean value obtained 

 was 28*332, which the author adopts as the most probable value 

 for the atomic weight of silicon. — J. Chem. Soc, li, 576, June, 

 1887. G. F. B. 



6. On the Atomic Weight of Gold. — Thorpe and Laurie 

 have made a very careful re-determination of the atomic weight 

 of gold, using for this purpose potassium brom-aurate, prepared 

 by the action of pure bromine in excess upon pure gold 



Am. Jour. Sci.— Third Series, Vol. XXXIV, No. 203.— Nov., 1887. 

 26 



