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POPULAR SCIENCE REVIEW. 
that there was considerable difference of opinion as to what should be re- 
garded as the firing point ; whether it was to be the temporary firing of the 
first small portion of oil vapour given off, or the permanent firing of the oil 
itself. Between these two results there might be a difference of from ten to 
twenty degrees Fahrenheit, according as the oil was tested in a shallow 
open basin, or a partially-closed vessel. In reference to the influence of the 
degree of inflammability of mineral lamp oil on the possibility of accidents 
occurring in the use of this material, it was shown that the mere volatility 
of the oil was not the only point to be considered, and that, apart from mis- 
use and carelessness, the construction of the lamps in which it was burnt 
was of considerable importance. To illustrate this, a lamp filled with what 
is commonly known as spirit or naphtha (the most volatile portion of pe- 
troleum or paraffin oil), was kept burning during the meeting. This lamp 
was so constructed, that there was no communication between the flame and 
the oil reservoir, except through the tube containing the wick, and conse- 
quently there was no chance of oil vapour or an explosive mixture of it with 
air coming in contact with the flame, so as to cause accident. Other kinds 
of lamps, in which there is free communication between the oil reservoir and 
the flame, afibrd less security, especially when the oil used in them vaporises 
at a low temperature. 
The Silvering of Mirroi’s. — Those who know anything of Liebig’s re- 
searches are aware that, for many years past, he has been engaged in trying 
to find a simple and satisfactory method of silvering glass for mirrors. After 
a long series of experiments, he has finally adopted the following process for 
silvering glass. The solutions employed are : — 1. One part of fused argentic 
nitrate dissolved in 10 of water ; 2. («), commercial nitric acid, free from 
chlorine, neutralised with ammonic sesquicarbonate, and diluted to sp. gr. 
1T15 ; or (h) 242 gr. ammonic sulphate dissolved in 1,200 c.c. water (sp. gr. 
1T05 to 1T06) 5 3. Solution of sodic hydrate, sp.gr. 1-050, prepared from sodic 
carbonate, free from chlorine ; 4. 50 grm. white sugar candy dissolved in little 
water, 3-1 gr. tartaric acid added, the mixture kept boiling for one hour, and 
diluted to 500 c.c. ; 5. 2-857 gr. dry cupric tartrate, covered over with 
water, and solution of sodic hydrate gradually added till solution has taken 
place, and solution made up to 500 c.c. These solutions are mixed in the 
following proportions: — 1st, 14 vol. of 1, 10 vol. of 2, and 75 vol. of 3=99 
vol. of (a) silvering solution ; 2nd, 1 vol.* 4, 1 vol. of 5, and 8 vol. of water 
=10 vol. of (b) reducing solution. The silvering mixture is then made by 
diluting 50 vol. of the silvering solution (a) with from 250 to 300 vol. of 
water, and adding 10 vol. of the reducing solution (b). If ammonic sulphate 
has been employed for solution (a), the liquid, after mixing the three in- 
gredients, must be allowed to stand three days before being used ; the clear 
liquor may then be drawn off. — Ann. Chem. Tharm. Suppl., v. 257. 
Lighting Street Lamps hy Electricity. — The Neiv York Twies contains an 
account of a simple but ingenious machine for this purpose, which it is pro- 
posed to employ in the American cities. It is a simple, small machine, 
placed in each lamp-post and connected by insulated wires with a central 
point, where the operator can, by simply starting the clock-work attached 
to the batteries, at once open the cocks in each lamp, and light up a whole 
city in the twinkle of an eye, or put out the lights at his pleasure. It 
