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 Thth part, instead of being a prin- cipal constituent, as authors have asserted.
Although it be very well known that the properties of the triple prussiates depend on the presence of an oxide of iron, the differeuces 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 properties of other saline bodies.
The facts observed by him have led him to consider the salts, hitherto 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 decomposition of ntriple 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 harytes by sulphuric acid, and obtains a fluid having all the characters of an acid, which forms directly with alkalies, earths, and oxides, the salts termed triple prussiates, and by superior aflinity 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 compound 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 instances, of double decomposition, and produces efl'ects altogether dissimilar to those of mere prussic acid.
The author observes also, that there are other substances beside
