182 ANNUAL OP SCIENTIFIC DISCOVERY. 



ish tint, which would interfere a little with the estimation of the last 

 few hundredths of copper. 



The above remarks also apply to arsenic, when present simulta- 

 neously with iron in the sample, as the nitric acid converts it into 

 arsenic acid, and this forms with the iron a salt, arseniate of iron, solu- 

 ble in ammonia. I have easily obviated this by adding to the nitric 

 or nitro-muriatie solution of the substance a little proto-salts of tin, or 

 sulphate of magnesia, as the arsenic is thus rendered insoluble, on 

 afterwards adding the ammonia. 



CEBTAIN METHOD OF ASSAYING COPPER BY ELECTRO-CHEMICAL ACTION. 



A GIVEN weight of the ore (as prepared for assaying by the dry 

 way) is dissolved in an acid (aqua regia is best) evaporated nearly to 

 dryness, redissolved in water, filtered, and then treated as the copper 

 solution described a little further on ; take 250 grains of the crystal- 

 lized bisulphate of copper, (or .half the quantity,) which contains 

 exactly 64 grs. of pure copper, dissolve it perfectly, add two or three 

 drops of acid, and place it in an unglazed earthen pot, which will hold 

 three fluid ounces ; place this in another, somewhat larger, glazed, in 

 which there is a weak solution of hydrochloric acid. Introduce a cop- 

 per cylinder (to which a wire is soldered, and whose exact weight is 

 known) in the copper-water, and an iron cylinder (with a wire simi- 

 larly attached) in the other vessel of acid and water ; amalgamate the 

 ends of the wires with nitrate of mercury, and connect them in a cup 

 of the same metal, or in any way, so that they are in perfect contact. 

 As soon as the circuit is perfected the operation will commence, and 

 will not cease until all the copper is precipitated on the copper cylin- 

 der, and which may be effected in from, ten to twelve hours. Then 

 take out the cylinder, dip it in water, dry and weigh it ; its increase 

 in weight will be the percentage of the copper, and in this case (for 

 half the quantity) it will be 32 grains heavier than before. The oper- 

 ation, when completed, can be known by taking one drop out of the 

 solution and placing it on pure gold, or platinum, and touching it with 

 a zinc rod ; if no copper be precipitated on the gold the solution will 

 be free from copper. Thus, then, may every one interested in the 

 produce of copper know the exact percentage of an ore according to 

 the sample. By the dry assay there is considerable loss, as proved, 

 by " check-samples, "on many occasions, varying from \ to | percent., 

 and yet the miner must sell by the dry assay ; and any one connected 

 with the sale of ore knows (especially in those of low produce) what a 

 difference one half per cent, makes in price. Chemical Gazette, March, 

 1851. 



ON THE PERMEABILITY OF METALS TO MERCURY. 



THE following is an abstract of a paper read by Professor Horsford, 

 before the American Association, Albany : 



Daniel observed that bars of lead, tin and zinc, became penetrated 

 by mercury, when partially or wholly immersed in it. He noticed that 

 a crystallized amalgam was formed in the case of each of the several 



