TRANSACTIONS OF THE SECTIONS. 45 



giving rise to the formation of Bodeker's salt (crystallized diphosphate of lime — 

 2CaO, HO, PO3 -f- 4 Aq). This suggestion received a practical trial at the 

 Houses of Parliament, in a competition to which five other candidates were 

 admitted by the Right Hon. the First Commissioner of Her Majesty's Works in 

 April 1864. 



Another promising scheme for the treatment of the decayed stone, especially 

 applicable to dolomite, consists in the employment of baryta conjointly with the 

 hardening salt, so that a base may be presented which is endowed with the power 

 of destroying the soluble sidphate of magnesia in the pores of the stone, forming 

 with it the remarkably insoluble sulphate of baryta, and at the same time engaging 

 the magnesia in one of its most diihcultly soluble combinations. On a recent 

 occasion tliis process was applied to some Caen-stone facings at St. John's Church, 

 Woolwich, which were badly decayed. Several examples of the application of 

 the superphosphate to decayed Caen, stone were referred to ; and with respect to 

 Portland stone, the earliest experiments were said to have been made at the Army 

 Clothing Establishment, Woolwich, where (in 1861) some decayed window-sills 

 were treated with perfect success. 



In connexion with the treatment of Portland stone, some interesting results 

 were then described, which serve to illustrate the increased hardness and strength, 

 and the diminished rate and capacity of water-absorption attending the employ- 

 ment of the superphospliate. By treating small cubes of Portland stone with the 

 phosphate solution, and when dry subjecting them to gradually increasing pressure 

 mitil crushed between plates of lead in the American Testing ^Machine at the 

 Royal Gun Factor}', it was found that the breaking weight of the stone was aug- 

 mented by 50 per cent. The increased hardness of the stone after treatment could 

 be readily ascertained by scratching with a pointed instrument of copper, which 

 metal proved to possess a degree of hardness intermediate between the original 

 and treated Portland stones. The porosity of the stone, as indicated by the 

 amount of water absorbed, proved to be greatly diminished in tlie case of the 

 treated cubes. The advantage of the process is most clearly apparent in the denser 

 and more compact variety of Portland known as the " Whit Bed," which alone is 

 employed for external building purposes ; that kno-wm as the " Base Bed," is softer, 

 and only lit for internal decoration, and its texture is so porous that in becoming 

 saturated it absorbs nearly 10 per cent, of watei'. Samples of Mansfield dolomite 

 absorbed amounts of water varying in difterent specimens from 6 to 8 per cent. 

 After treatment by this process, the degree of absorption was reduced one half, aud- 

 the results were even more favourable in the case of Caen stone. The cost of 

 materials employed in the treatment of stone according to this plan is very trifling, 

 and bears but a small proportion to the cost of labour necessarily expended upon 

 the cleaning and preliminary preparation of the stone before the solution can be 

 applied. One gallon of solution will cover about 250 feet superficial, when two 

 coatings are applied upon Caen or Portland stone. Tlie superphosphate employed 

 must not contain any appreciable amount of sidphuric acid, and the specific gravity 

 of the solution, when diluted for use, should be about I'l. 



On certain Neiv Processes in Photographj. By John Spillee, F.CS. 



. Under this head were described several interesting improvements in photography, 

 based on the chemistry of gelatine. The processes to which reference was made 

 were the various modifications of the Woodbury tj'pe, including the new method 

 of micro-photo-sculpture, the art of photolithography, as practised in the Ro3al 

 Arsenal at ^^'^oolwich, and some illustrations of the use of gelatine or albumen, on 

 a foundation of silk, satin, or cambric, the work of Mr. H. B. Pritchard, of the War 

 Department. The Hon. H. Fox Talbot was one of the first to describe and make 

 a practical use of the action of light upon a mixture of gelatine and a soluble 

 bichromate, and after him Col. Sir H. James, Mr. Swan, of Newcastle, and Mr. 

 Woodbury, of Manchester, have applied the same chemical principle in new direc- 

 tions. It is Imown that the chemical rays of light have the effect of rendering 

 insoluble gelatine to which a bichromate has been added ; and it would appear that 

 this oxidizing salt hardens the animal substance by forming with it a combination 



