1862.] 



159 



Owing to the frequent occurrence of thallium in copper ores, it is 

 very probable that this element may sometimes be present in com- 

 mercial copper, and may give rise to some of the well-known, but 

 unexplained, differences of its quality. I am at present engaged in 

 investigating this subject, and have already found some indications of 

 thallium in commercial products. 



I have no hesitation in saying that in some of our large copper, 

 sulphur, and sulphuric-acid works, thallium is at the present time 

 being thrown away by the hundredweight : a very slight modifica- 

 tion of the present arrangements of the furnaces and condensing 

 flues, or even an examination of some of the residues, would enable 

 nearly the whole of this to be saved. Bearing this in view, I am 

 now in communication with several large consumers of thalliferous 

 minerals. My applications have without exception been met with 

 the utmost courtesy and most obliging offers of assistance, and there 

 is therefore every probability that I shall soon have an opportunity 

 of preparing this new element in considerable quantities, and thus be 

 enabled to pursue the investigation with more comfort and accuracy 

 than hitherto, when my stock of material has had to be counted by 

 the grain. 



IX. " On the Photographic Transparency of various Bodies, and 

 on the Photographic Effects of Metallic and other Spectra 

 obtained by means of the Electric Spark." By Prof. W. 

 ALLEN MILLER, M.D., LL.D., V.P. and Treas. R.S. Re- 

 ceived June 19, 1862. 



(Abstract.) 



In this paper the author pursues an inquiry the commencement 

 of which was communicated to the Chemical Section of the British 

 Association last year. Owing to the employment of a prism of bi- 

 sulphide of carbon, he was then led to believe that the photographic 

 effects of the electric spectra produced by the different metals were 

 in a great degree similar, if not identical. Subsequent investigations 

 have, however, shown him that the absorbent effects of the bisul- 

 phide upon the chemical rays are so great, that the conclusions then 

 drawn from observations made by this refracting medium require 



