Chemistry and Mineralogy. 399 



exhibiting a strong action with caustic potash. It was suggest- 

 ed, that the first fluid was acetate of methylene, the specific 

 gravity of which is .919, and the boiling point 136°. The 

 arguments of Mr Scanlan were admitted by the Section to be 

 conclusive in favour of the substance being distinct from pyro- 

 acetic, or pyroxylic spirits. 



23. Mr Moor mentioned a curious circumstance in reference 

 to the corrosion of lead pipes. The worm of a still used for 

 preparing medicated waters, was exhibited, which was corroded 

 completely through its substance, at those points where it had 

 been supported with wood and tied with twine. At these points 

 a black substance was formed, consisting of oxide and chloride 

 of lead. It was obvious that the effect was to be attributed to 

 galvanic action. 



24. Dr Barker described a new mode of separating the per- 

 oxide of iron by means of acetate of potash. The latter salt, 

 when added to a solution of per-salt of iron, precipitates the 

 peroxide when the liquid is boiled. This would appear to afford 

 an elegant method of separating iron from manganese. He 

 made an observation relative to the precipitation of magnesia by 

 phosphate and carbonate of ammonia ; viz. that the same pre- 

 cipitation takes place with bi-carbonate of potash, and other 

 salts. 



25. Dr Geoghehan suggested the advantage of employing the 

 double salt of iodide of potassium and bicyanide of mercury, for 

 the purpose of detecting muriatic acid in prussic acid. Sul- 

 phuric acid is frequently met with in prussic acid, but the dis- 

 tinction between these two acids is readily made, by means of 

 nitrate of barytes. The peroxide of mercury, usually employed 

 for testing the purity of prussic acid, is ambiguous in its action, 

 as it is usually impure. The use of this salt is not applicable' 

 to the alcoholic prussic acid. 



26. Mr Johnston made some observations on the iodides of 

 gold, which he had analyzed. Their composition is similar to 

 the chlorides. Previous errors, he found, were to be ascribed 

 to the precipitation of an excess of gold, when ammonia was 

 employed in the analysis. There are three compounds, viz. 

 (1.) Au I ; (2.) Au 3 I ; (3.) Au 3 I -}- KI, the atom of gold 

 being 25. 



d d 2 



