510 



of the wall with a plate of glass, well cemented round on all sides ; 

 and it appeared evident that the whole quantity formed under these 

 circumstances, was nearly equal to that which usually formed on the 

 same surface when exposed to the free action of the atmosphere. 



The author concludes this paper with an analysis of the stone of 

 which the laboratory is built, showing that it contains 96 per cent, 

 of carbonate of lime, the rest being sand, oxide of iron, ochry clay, 

 with a trace of animal matter, which is conceived to be from the 

 shells contained in the stone. 



He also gives the result of his experiments on the nitre collected 

 in this situation, which shows that the quantity of calcareous salt 

 contained in it does not exceed -j-J-^th part, instead of being a prin- 

 cipal constituent, as authors have asserted. 



On the Nature of the Salts termed triple Prussiates, and on Acids 

 formed by the union of certain Bodies with the Elements of the 

 Prussic Acid. By Robert Porrett, ./. Esq. Communicated by Wil- 

 liam Hyde WoUaston, M.D. Sec. R.S. Read June 30, 1814. [Phil. 

 Trans. 1814,;?. 527.] 



Although it be very well known that the properties of the triple 

 prussiates depend on the presence of an oxide of iron, the differences 

 between these and the simple prussiates in being neutral, and with 

 difficulty decompounded, are by no means explained ; and the object 

 of the author is to reconcile these anomalies with the general pro- 

 perties of other saline bodies. 



The facts observed by him have led him to consider the salts, hi- 

 therto termed triple prussiates, as binary salts consisting of a single 

 base, combined with a very compound acid, in which iron enters as 

 a constituent along with the elements of prussic acid. The leading 

 experiments on which this opinion is founded are two ; first, the de- 

 composition of a triple prussiate of soda by the voltaic battery, which 

 occasions the alkali to go alone to the negative pole, and carries the 

 iron not to the negative as a base, but to the positive pole, as one of 

 the elements of the acid part of the salt. In a second experiment he 

 decomposes a triple prussiate of barytes by sulphuric acid, and ob- 

 tains a fluid having all the characters of an acid, which forms di- 

 rectly with alkalies, earths, and oxides, the salts termed triple prus- 

 siates, and by superior affinity displaces carbonic and acetic acids 

 from their combinations. 



By distillation this acid may be decomposed into prussic acid and 

 oxide of iron, which has therefore been thought to be present as a 

 base, by those who have overlooked the circumstance of the com- 

 pound being acid, and in fact a much stronger acid than the prussic 

 acid itself. Accordingly, when it is not exposed to too great a heat, 

 this acid is transferred entire from one base to another, in many in- 

 stances, of double decomposition, and produces effects altogether dis- 

 similar to those of mere prussic acid. 



The author observes also, that there are other substances beside 



