liquid having been drained off was passed through a charcoal filter, as adopted by Newbery and Vautin.  The manager, Mr. Wesley Hall, stated that he estimated cost per ton was not more than 30s., and he expected shortly to reduce that when he began making his own sulphuric acid.  As he was obtaining over 4 oz. to the ton the process was paying very well, but it will be seen that the price would be prohibitive for poor ores unless they could be concentrated before calcination.

The Pollok process is a newer, and stated to be a cheaper mode of lixiviation by chlorine.  It is the invention of Mr. J. H. Pollok, of Glasgow University, and a strong Company was formed to work it.  With him the gas is produced by the admixture of bisulphate of sodium (instead of sulphuric acid, which is a very costly chemical to transport) and chloride of lime.  Water is then pumped into a strong receptacle containing the material for treatment and powerful hydraulic pressure is applied.  The effect is stated to be the rapid change of the metal into its salt, which is dissolved in the water and afterwards treated with sulphate of iron, and so made to resume its metallic form.

It appears, however, to me that there is no essential difference in the pressure brought to bear for the quickening of the process.  In each case it is an air cushion, induced in the one process by the pumping in of air to a cylinder partly filled with water, and in the other by pumping in water to a cylinder partly filled with air.

The process of extracting gold from lode stuff and tailings by means of cyanide of potassium is now largely used and may be thus briefly described:—­It is chiefly applied to tailings, that is, crushed ore that has already passed over the amalgamating and blanket tables.  The tailings are placed in vats, and subjected to the action of solutions of cyanide of potassium of varying strengths down to 0.2 per cent.  These dissolve the gold, which is leached from the tailings, passed through boxes in which it is precipitated either by means of zinc shavings, electricity, or to the precipitant.  The solution is made up to its former strength and passed again through fresh tailings.  When the tailings contain a quantity of decomposed pyrites, partly oxidised, the acidity caused by the freed sulphuric acid requires to be neutralised by an alkali, caustic soda being usually employed.

When “cleaning up,” the cyanide solution in the zinc precipitating boxes is replaced by clean water.  After careful washing in the box, to cause all pure gold and zinc to fall to the bottom, the zinc shavings are taken out.  The precipitates are then collected, and after calcination in a special furnace for the purpose of oxidising the zinc, are smelted in the usual manner.

The following description of an electrolytic method of gold deposition from a cyanide solution was given by Mr. A. L. Eltonhead before the Engineers’ Club of Philadelphia.