306 Presence of Arsenic and Antimony in Streams and Rivers. 



exactly as I have described in testing the acid, only, instead of a 

 drachm, I use a less quantity, proportionate to the acid used and 

 the distillate obtained. After one piece of copper is coated, it is 

 withdrawn and another substituted, and so on until no more 

 coating takes place ; much evaporation of the liquid is made up 

 from time to time by a little boiling water. 



When antimony is in the distillate, it deposits more readily 

 than the arsenic upon the copper, and the first pieces coated 

 have more of a purple or blue tint than the steel-grey colour of 

 the arsenic. 



The remainder of the distillate may be tested by a Marsh's 

 apparatus, heating the gas as it passes through a quill-tube 

 drawn to a fine point, in order to get the metallic arsenic de- 

 posited upon the tube. 



The metallic arsenic, deposited in this way from the residue of 

 the distillate from two ounces of the sand, is in many instances 

 of sufficient quantity to dissolve or sublime and examine by other 

 tests. 



The sands which I have examined have been selected with 

 much care ; and in most cases, when taken from the beds of streams 

 or rivers, they have been taken above where they could receive 

 contamination from coal-pits or works, or contamination of any 

 description whatever : I append a list of them, in order that any 

 one may repeat the experiments. 



I am indebted to Mr. Woodcroft, of the Great Seal Patent 

 Office, for the first eight specimens, and to Mr. George Phillips, 

 of the Inland Revenue Laboratories, for the next four specimens, 

 both these gentlemen having taken much interest and trouble in 

 the matter. For most of the other specimens I am indebted to 

 kind friends, and one or two I have procured myself. 



List of Sands examined. 



From Cragg Hall, Cheshire. 



From Black Brook, which falls into the Dane, Staffordshire. 



From the source of the Wye, the Buxton Water supply. 



From the source of the Goyte, Derbyshire. 



From Oaks Clough Redmires, supply of Sheffield. 



From the source of the River Porter, Fulwood, Sheffield. 



From Hog Shaw Brook, Buxton. 



From the source of the River Dove, Derbyshire, where it issues 



from a compact limestone, rock at Mr. Marsden's Dowal. 

 From Middle Lake, Dinish Island, Killarney, Ireland, County 



Kerry. 

 From Flesk River. 



From Flesk River, Killarney, Ireland, County Kerry. 

 From Ogiven River, near Penrhyn Slate Quarries, about four or 



