M. Leroux on Refractive Indices of Vapours. 297 
Sulphur: 6: ow, L00L629 
Phosphorus . . . 1:001864 
PASORITCH 02 ¥5, he eet tal DOT 
Merenty .)) 6 0 sie 1000896 
The apparatus by which these results were obtained consists 
of a very large furnace mounted on an axis, and provided at its 
lower part with a divided circle, by which it can be inclined at 
any angle. In the centre of the furnace there is a prism analo- 
gous to that of Borda, employed by Dulong. This prism is made 
of solid iron, and the rays enter and emerge through glass plates 
cemented by a method peculiar to M. Leroux. The exact mea- 
surement of the angle of the prism presents some ingenious 
points. As in Babinet’s goniometer, the light is concentrated 
on the prism, while filled with the vapour, by a telescope, and the 
light on its emergence is received on another telescope provided 
at its focus with a micrometric wire. With the first telescope, 
its distance from the furnace, the size of the furnace, the distance 
of the second telescope and its focal distance, which is above 2 
yards, the extent of this gigantic goniometer is about 23 feet. 
The means of verifying the results leave nothing to be desired. 
Rose*, in a paper on the separation of tin from other metals, 
and on its quantitative estimation, describes the following method 
of effecting these objects. 
The separation of tin from other metals is usually effected by 
oxidation with nitric acid, so as to convert the tin into stannic 
acid: in certain cases, however, this method gives inaccurate 
results, and can only be said to be quite successful in the case 
of the strongly basic oxides. 
Another method consists in dissolving the binoxide of tin in 
hydrochloric acid, and precipitating by sulphuric acid. Both 
modifications of binoxide are precipitated im this manner, in the 
presence of a large excess of water. The precipitates require a 
long time in order to settle completely, more especially when 
there is a large quantity of free hydrochloric acid. The precipi- 
tate must be carefully washed free from hydrochloric acid other- 
wise when it 1s ignited some tin cscapes in the form of chloride. 
The ignition is best effected with the addition of some carbonate 
of ammonia. 
In the presence of certain substances, phosphoric acid for 
example, even this method gives inaccurate results. The pre- 
sence of a large excess of hydrochloric acid does not hinder the 
precipitation of some phosphoric acid along with the binoxide 
of tin. 
When tin is to be separated from other metals, it must be 
* Poggendorfi’s Annalen, January 1861, 
