92 REPORT — 1861. 



acid being left behind, which is purified by distUlation. The acid thus obtained is 

 in appearance not to be distinouished from oil of vitriol, being a colourless, heavy, 

 thick, oily, corrosive liquid, giving oif on heating dense white fumes. By heating 

 the iiqueous perchloric acid with four times its volimie of concentrated sulphuric 

 acid, the latter takes water from tlie first, dense white fumes are evolved, a yellow 

 mobile liquid distils over, and afteiTvards thick oily drops appear, which, when 

 coming in contact with the yellow liquid, form the white crystals, previously obtained 

 by SeruUas, but in such small quantities that he was miable to analyse the substance, 

 which prepared in this way always contains sidphuric acid, and is therefore not 

 fit for analysis and requires redistillation. Heated, however, to 110° C, the cry- 

 stals decompose and split up again into the yellow liquid, which distils over at a low 

 temperature, and the thick oily liquid, which remains in the retort. The yellow 

 liquid thus obtained is pm-e perchloric acid, CI 0, H, a body not known before, which 

 can be obtained also by distilling one atom of perchlorate of potassium with foiu* 

 atoms of sulphiu'ic acid. In the pure state it is perfectly colourless, but as com- 

 monly prepared it is slightly yellow, ovnng to the presence of lower oxides of 

 chlorine. Perchloric acid is one of the most powerful oxidizing agents known : a 

 single drop brought into contact with charcoal, paper, wood, alcohol, &c., imme- 

 diately causes explosive combustion, in violence not falling short of the decomposi- 

 tion of chloride of nitrogen ; and brought on the skin wounds are produced, which 

 do not heal for weeks. Like nitric acid it cannot be distilled without decompo- 

 sition, but it darkens, and ultimately decomposes with explosion. It cannot be kept 

 for any length of time ; for even when sealed up in glass bidbs which are placed at 

 the ordinary temperature in the dark, it decomposes suddenly after some time, 

 breaking the vessel containing it. It mixes with, water with a hissing noise and 

 evolution of heat, forming the same crj^stals which were mentioned before, and were 

 used for preparing the piu-e acid. These crystals are the monohydrated perchloric 

 acid, 01 Og H+Hj 0^. They melt at 50° C, and heated to 110° C. split up in pure 

 perchloric acid, which distils over, and an oily liquid boiling at 200°, which is 

 also obtained by boiling aqueous perchloric acid tiU dense white fumes are given oft*. 

 This oily acid has a constant composition, containing 72'3 per cent, of pure per- 

 chloric acid and 27'7 per cent, of water. This per-centage corresponds, however, 

 to no definite hydrate of simple atomic composition ; and therefore this acid fol- 

 lows the same general relations respecting composition and boUing-point which, 

 as I have shown previously, hold good for so many other aqueous acids, namely, 

 that the phenomenon of constant boiling-point and constant composition depends 

 chiefly upon physical and not upon chemical attractions. 



On Vesicular Structure in Copper. By Drs. Eussell and Mattbxesseh-. 



The authors proved by numerous experiments that the vesicular structm-o is 

 caused by the action of carbon or sulphur on the suboxide dissolved in melted 

 copper. 



On certain Difficulties in tJie ivay of separating Gold from Quartz. 

 By Dr. Smith of Sydney. 



In Australia the usual plan is to reduce the quartz to powder by Cornish stampers, 

 a stream of water being allowed to flow through the stamp box dm-ing the opera- 

 tion. The pounded quartz is carried by the stream through fine gratings, and then 

 along an inclined plane supplied with various contrivances, such as blanket stuff 

 and plates of copper rubbed over with morciu-y, for detaining the gold. The stream 

 is next conducted into the basin of a Chilian mill, where the "pulp " is ground up 

 with mercury. These operations are for the most part so successful as to leave not 

 more than half an ounce of gold in a ton of " tailings." But this successful result 

 is only attained when the quartz is free from pyrites. When pjTites is present, 

 particularly a black amorphous variety (found by Dr. Leibius to contain disulphido 

 of copper and sesquisulphide of iron), there is a notable loss both of gold and 

 mercury in the process of amalgamation. In the basin of the Chilian mill a greyish- 

 black scum might then be seen, which contains mercury and gold in fine di^-ision, 

 together with various components of the pyritous quartz, buoyed up by the en- 

 tanglement of air. The action upon the mercury appeared to be chiefly mechanical, 



