Presence of Arsenic and Antimony in Streams and Rivers. 305 



qualitative tests. I have not directly estimated quantitatively 

 the arsenic in any one instance ; nor do I think that by the pro- 

 cess which I follow to detect the arsenic, and which I shall give, 

 should I get, in most instances, if not in all, anything like the 

 quantity which the sand contains. 



The process which I adopt is as follows : — The sand is first 

 dried by means of a bath at not too high a temperature, and 

 sifted, if necessary, through a coarse sieve, to remove anything 

 larger than sand ; the portion for the experiment I then weigh 

 out. I seldom require more than two ounces of the dry sifted 

 sand. I then ascertain that my hydrochloric acid is free from 

 arsenic (or rather how far it is contaminated with it, for it is 

 rarely indeed that this acid is found entirely free from arsenic), 

 which I do by introducing into a drachm of the acid diluted with 

 about three 'drachms of distilled water, when brought to boil in a 

 small flat-bottomed flask, about the eighth of a square inch of 

 bright copper-foil, specially prepared as free from arsenic as it is 

 possible to be obtained*, and gently boiling the same from about 

 half an hour to three-quarters or so, avoiding much evaporation 

 by having a small funnel in the mouth of the flask. Should this 

 piece of copper get coated with arsenic, I take it out and replace 

 it by a similar piece, and boil it in a similar manner ; should this 

 piece likewise get coated, I should scarcely like to use such im- 

 pure acid ; but if no coating has taken place, or only one piece 

 was coated, I measure out into a small flat-bottomed flask (a flask 

 capable of holding about three liquid ounces is the size I prefer), 

 half an ounce of the acid, and gradually add to it the two ounces 

 of the dry sifted sand. I now close the bottle with a cork, and 

 allow it to stand for some hours until the acid has thoroughly 

 penetrated the sand, when I remove the cork, and at once attach, 

 by means of a perforated cork, a bent tube about 3 feet long, 

 leading into a receiver through a cork, a little loose at first, but 

 capable of being made tight afterwards, the receiver being placed 

 in water. Heat is now applied by means of a sand-bath, gently 

 at first, gradually increasing when the cork at the receiver is 

 made to fit tight. I also apply wet rags or bibulous paper 

 down the tube. In about an hour the greater part of the distil- 

 late will have passed into the receiver, when it may be detached. 

 The distillate, which varies in quantity according to the nature of 

 the sand, I measure. I have found it to average 190 grains; 

 but, as stated before, it varies in quantity according to the nature 

 of the sand. 



The test which I generally first apply is the copper one, 



* I have lately examined a great many specimens of copper said to be 

 free from arsenic; of these, eight specimens were electrotype, but in all I 

 found arsenic. 



