Mr. J. Napier 07i Damp Walls. 333 



dfed measures is made up in the usual manner with 21"4 grains of pure 

 and dry bichromate of potash. The chromate solution is then added to 

 that of the yellow prussiate until a blue tint is no longer produced with 

 a solution of perchloride of iron, spotted on a white slab. 'J'he number 

 of divisions consumed multiplied by two, gives the per centage amount 

 of pure crystallized yellow prussiate. 



The author has not yet been able to explain tlie action in a satisfactory 

 manner. Eed prussiate is undoubtedly one of the products (for it can 

 be obtained in crystals by evaporation), yet the amount of chromic acid 

 consumed by experiment, shows that the action is more complex, and 

 that some other compound is likewise formed. When a caustic alkali 

 is added in slight excess to the mixture obtained as above, the chromic 

 acid and yellow prussiate are reproduced, so that the oxide of chromium 

 cannot be separated by this means. From numerous and careful experi- 

 ments, it was found that 100 grains of crystallized yellow prussiate are 

 invariably decomposed by 10"7 grains of bichromate of potash. 



Wlien the " prussiate cake," or a liquid containing alkaline sulphide, 

 is the subject of experiment, a modification of the process is required, 

 but it is not considered necessai-y to enter into the details in the present 

 communication. 



Mai/ 3, 1854 (the Concluding Meeting of the Session was held this 

 evening). — The President in the Chair. 



TuE Council was authorized to appoint in due time delegates to attend 

 the next meeting of British Association in Liverpool, and present the 

 Society's invitation to visit Glasgow in 1855. 



Mr. J. Napier then read a paper on — 



DAMP WALLS. 



In the paper I had the honour of reading to the Society last session 

 upon Sandstones used for building purposes, I stated my intention of 

 bringing the subject of damp walls in houses under your notice. The 

 subject of damp walls was so closely connected with the investigations in 

 last paper that I could not avoid having my attention specially drawn to 

 it, and I therefore resolved, from the importance and probable bearing 

 upon the health of the community, or, at all events, the health of those 

 who are living in damp houses, to devote a little time to its consideration. 

 And in communicating to you the results of these inquiries, I will 

 do so in ^the order in which I conducted the inquiry, first, by con- 

 sidering the nature of the materials used in the construction of houses, 

 and second, the question of damp wails. The materials used in building 



