Artificial Silicification of Limestones. 119 
ness of more than 2 centimeters (8 tenths of an inch). 
nufaciure al-Ammoniac fro e residues of gas works.— 
The Industrial Society of Mulhausen offers nually a number of pri- 
acal liquid of gas works. The main difficulty in the operation consis 
in separating the tar-like material which it contains. The following is 
d 
densed. In this state it is nearly free from its impurities ; it is neutral- 
ized with chlorohydric acid and evaporated in a lead boiler. As it de- 
posits it is withdrawn by means of a wooden rake; it is allowed to 
drain, and then introduced into a brick mould and subjected to strong 
pressure. Blocks of sal-ammoniac are thus obtained, which are dried 
in an oven heated by part of the heat furnished by the evaporating fur- 
nace. 
Separation of bromine from iodine.—Balard’s process, as carried on 
by M. H. de Luca, gives a method of recognizing traces of iodine and 
of a milligram of iodine. . 
Artificial Silicification of limestones.—It is some years since M. 
Kuhimann of Lille proposed to preserve pieces of sculpture, etc., by 
impregnating them with a solution of silicate of potash. 3 KO 
CO? CaO=Si0* Ca0-+CO2 KO. This process has been used on a 
grand scale in certain parts of the cathedral Notre Dame. The archi- 
tect of the cathedral reports as follows: 1, that the infiltration of silica 
made “sur les terrasses et contre-fort du choeur,” in October, 1852, 
have preserved the stone fi the green moss that covers stones in 
Moist places: 2, that the gutters and flagging of limestone subjected to 
'§ process present surfaces perfectly dry, covered with a silicious 
Crust: 3, that upon the stones so prepared, dust and spider webs are 
