in Lead and its Compounds. 127 



visible specimen of burnished gold obtained in each experiment 

 has been preserved in a hex-metically sealed tube. 



The diffusion of goldj as proved by the experiments in ques^ 

 tion, is at least curious, and may probably suggest chemical 

 and geological considerations of special interest at the present 

 time. The fact of gold existing in certain soluble compounds of 

 lead is remarkable ; and it may be that sea-water will one day 

 be found to contain the precious metal, though in infinitesimaUy 

 small proportion. 



The quantity of gold obtained in each experiment was far too 

 minute io be capable of estimation by the most delicate balance. 

 In order, however, to give an approximate and comparative 

 notion of the quantities respectively extracted, the following 

 scale of comparison will be adopted in the description, — trace, 

 minute trace, very minute trace, and just perceptible trace. 



At present it has not been possible to prepare lead free from 

 a trace of gold. 



Method of Examination. 



The lead was separated from the compounds of lead examined 

 by a process of reduction described under each experiment ; a 

 known weight of the lead was then submitted to the process of 

 cupcUation in the usual way, and the button of silver left after 

 cupellation was carefully detached from the cupel, flattened under 

 a hammer to free it from adherent matter, transferred to a small 

 watch-glass, treated first with very dilute nitric acid at a very 

 gentle heat until all action had ceased, and then with strong 

 nitric acid. The black residual matter was carefully washed 

 with distilled water by decantation, transferred to a small piece 

 of writing-paper, dried at a gentle heat, rubbed with a steel bur- 

 nisher, gummed to the paper, and preserved in a small glass 

 tube hermetically sealed. \Vhen necessaiy, this process was per- 

 formed under a microscope. 



Lead. 



Exp. I. A si)ecimen of lead pipe from the Great Exliibition of 

 1851. Cupelled 2000 grs., the button obtained, treated with 

 nitric acid, left a i7-ace of gold. 



Exp. II. A specimen of " Pattinson's crystallized lead." Cu- 

 pelled 2000 grains, treated the remaining button with nitric acid, 

 and obtained a minute trace of gold. 



Eocp. III. S])ecimcn of lead i'rom the Ncnthead Works near 

 Alston. Cupelled 2000 grs., the button obtained, parted with 

 nitric acid, left a very minute trace of gold. 



Exp. IV. Specimen of lead from Tuscany, from the Great 

 Exhibition of 1851, hard and brittle, witii a close-grained cry- 



