37 
colouring matter. Mr. Procter, after mentioning the use of other sili¬ 
cates, then proceeded to speak of the processes of Field and Bernhays, 
of Crooke and of Jesse Rust, who proposed to use hydro-fluoric acid or 
hydro-fluo-silicic acid alone, or with various saline compounds, and also 
of that of Mr. Spiller, who, by the use of a wash of superphosphate of 
lime, proposes to deposit phosphate of lime on stones as the hardening 
and preservative material. The paper was concluded with extracts from 
the report of the Government chemical committee, composed of Dr. 
Hoflfman, Dr. Frankland, and Mr. Abel, who seem to think that the 
experiments have not sufficiently stood the test of time to enable them to 
give a decided recommendation to any process, but say that several of 
the processes included in the first two subdivisions (the silicating pro¬ 
cesses) ** will in the course of a few years furnish ample data for correct 
conclusions regarding their applicability, for the only conclusive test is 
that of actual application and protracted exposure to the corrosive 
influence of a London atmosphere.^' 
