1. Since the date of the last paper on Thallium which I had the honour of communicating to the Royal Society, I have been unremittingly engaged in attempting to find, a source from which this metal could be extracted in quantity. Having first discovered thallium in the deposit from the chambers of a sulphuric-acid manufactory, I naturally turned my attention towards similar deposits from English oil-of-vitriol works where pyrites was burnt. Applications were accordingly made to several large manufacturers for specimens of the pyrites which they used, and also for some of the deposit from their leaden chambers. These requests, with scarcely an exception, were readily responded to, and in a short time I was in possession of specimens from nearly thirty different establishments. In many instances thallium was detected in the pyrites, but I was disappointed to find that the deposits of sulphate of lead from the chambers contained no thallium whatever. I then applied to manufacturers who I had ascertained were constantly burning thalliferous pyrites, and obtained from them specimens of the products in different stages of their manufacture, but in no instance did I find an accumulation of thallium in any part of the operations. 2. In the operation of burning the pyrites, the thallium oxidizes with the sulphur and volatilizes into the leaden chambers; it there meets with aqueous vapour, sulphurous and sulphuric acids, and becomes converted into sulphate of the protoxide of thallium. This being readily soluble both in water and dilute sulphuric acid, and not being reduced by contact with the leaden sides, remains in solution and accompanies the sulphuric acid in its subsequent stages of concentration, &c. It is not probable therefore that any thallium can accumulate in the insoluble deposit, but it will remain dissolved in the liquid, where indeed I have found it—not however in quantities sufficient to be worth extracting, as it is present in scarcely a larger proportion than in the original pyrites. That this view of the path followed by thallium is correct, I am satisfied both from careful analyses of products from various manufactories, and also by experiments tried on a small scale in my own laboratory. M. Lamy states that he extracts thallium from similar deposits to those which I have examined; but as I have experimented on residues from English manufactories in which they burn pyrites almost, if not quite, as rich in thallium as that used in M. Kuhlmann’s works, there must be some cause or local arrangement in their manufactory, different from what is usually adopted in this country, to occasion so large an accumulation of thallium at one particular stage of the operations.