SCIENTIFIC SUMMARY. 
113 
takes place in them. This is probably owing to the air never having 
been completely driven out by the steam in the boiling, or to some making 
its way again into the cases before they are soldered down. Mr. M‘Call 
effects the absorption of any remaining oxygen by placing in the top of 
his cans a fused lump of hyposulphite of soda, which, being exposed when 
the can is soldered, is expected, by the decomposition familiar to chemists, 
to absorb any oxygen left in the vessel. 
Carbolic acid, one of the multitudinous bodies obtained in the destruc- 
tive distillation of coal, has recently been discovered, by Mr. Ashby, to 
possess certain properties which will no doubt be applied before long to 
many useful purposes. It seems to be diametrically opposite to oil in its 
effect upon rubbing surfaces : just as oil is anti-frictional, so carbolic acid 
is pro-frictional ; or, to state it more definitely, as oil appears to keep 
moving surfaces asunder by interposing a thin film between them, so 
carbolic acid appears to make them bite and bind by bringing them into 
absolute contact. The effect may be at once observed by placing a little 
of the acid upon a perfectly clean and dry oil-stone, and then rubbing the 
face of a knife upon it. The sensation of the bite is very curious, and 
gives the impression of the stone and the steel having absolutely nothing 
between them, or even as if they were positively brought together by 
some attractive force. The property of carbolic acid may be advantage- 
ously applied to the operations of grinding, filing, boring, and sawing, in 
metal. 
A harmless green pigment, fit to be employed in confectionery, has long 
been a desideratum. The following has been suggested as being perfectly 
harmless, and capable of replacing the very poisonous arsenite of copper. 
Thirty-two parts of saffron are infused, for twenty-four hours, in 700 
parts of distilled water. Then take 2G parts of carmine of indigo, in- 
fused in the same manner in 156 parts of distilled water. Upon mixing 
the two liquids together, a very beautiful green is obtained, which will 
colour a hundred times its weight of sugar in a very perfect manner. 
The colour may be preserved for a long time, either by evaporating the 
liquid to dryness, or by converting it into a syrup. 
An improvement in silvering glass, which possesses some advantages over 
the process known as Liebig’s, has been published by Mr. Cimeg. He 
employs a mixture of ammonia-nitrate of silver and Rochelle salt. This 
is poured carefully upon the sheet of glass, which has been previously 
cleaned with a weak solution of Rochelle salt. For a few minutes the 
mixture begins to get turbid, and after another two minutes, silver deposits 
on the surface of the glass. In about ten minutes the glass-plate will be 
covered, and, in about thirty minutes, enough silver (about 60 grains per 
square yard) will be deposited for most purposes. The mixture is then 
to be poured off, the silvered plate of glass washed four or five times in 
water, and then set up to drain and dry. When dry, it must be varnished, 
when the glass is ready for framing. 
The metal cadmium has as yet been applied to very few uses. The 
brilliant yellow colour of its sulphide is largely employed as a pigment, 
but w’e can scarcely point to any other practical application of it. It 
has recently been proposed as an addition to pyrotechnic displays. By 
VOL II. — NO. V. I 
