C—3

118

" Having now partially described and ascertained the nature of our said invention, and in what manner the same is to be performed, we declare that what we claim is— " 1. In a percussion table, the herein-described means of guiding the travelling-band by strips of wood attached to its outer surface, and guided in a channel iron above. " 2. In a percussion table, attaching the feeding-boxes, jet-pipes, and distributing-table edged with fabric to the movable frame, substantially as described. "3. The combination of three or more percussion tables arranged with communicating channels so as to constitute a compound machine for successive treatment of the material without requiring manipulation thereof, substantially as described. " Dated this 16th day of October, 1890. " Carl Luhrig. " John Charles Cunninghame." " Certified to be a true copy—Whitaker and Russell, solicitors in New Zealand for the applicants."

Cyanogen Process for Extracting Gold and Silver. This process has been used now in New Zealand for a considerable time with good success by the Cassell Company and also by the Sylvia. As will be seen by the results hereinbefore stated in connection with the treatment of the ore from the Sylvia Company's mine, it is certainly the most effective process yet introduced into this colony, and no doubt would be more generally used were it not for the prohibitive royalty the company exacts from those who erect one of their plants. But the question of extracting gold and silver by dissolving these metals in a cyanide solution is not confined altogether to the Cassell Company. Another patent right has been granted to W. D. Bohm for a different method of applying the cyanide solution, and, judging from an examination of his plans, Mr. Bohm's appliance is in some respects superior to the Cassell Company. It is stated by some mining men in the Thames that cyanide of potassium will not act effectually on some ores, especially on those containing a large percentage of iron and manganese, also on gold coated with oxides of these metals ; but it has been clearly proved by the work already done by the Crown and Sylvia Companies at their works that there is nothing in this contention. The following interesting article appeared in the Journal of the Chemical Society, written by J. S. McArthur, the chief moving spirit in the Cassell Company :— " The Cyanide Process. — The McArthur-Forrest System of Gold Extraction." " In order to understand the present systems of gold extraction, to properly appreciate the work already done, and to gauge the difficulties to be surmounted, it is necessary for us to look back and trace the connection between the known forms of gold as found in Nature and the methods used to separate it from its base environments. " In the earliest ages gold would naturally only be found in nuggets and grains (our word carat is derived from ,& Bersian word meaning a grain), which required no means of separation beyond picking vp —happy age when gold had only to be picked up ! " From grains the ancient would come down to gold dust, and this was no doubt separated from the sand or earthy matter with which it was associated by the skilful use of air currents, which were caused to blow away the sand, leaving the precious metallic dust. This method is still practised in Arabia and the East. Wherever water was plentiful it was found that it did the required separation better and more economically than air, a method of separation which has been and still is in use everywhere all over the world. The prospector, digger, explorer, and even the tourist nowadays provides himself with a ' pan' in which to wash a sample of ' Ji: t' at the nearest stream. From the pan comes the ' cradle,' ' long torn,' and the innumerable mechanical arrangements for the separation of gold from earthy matters. Up to this point we have only mechanical means of separation which depend on the high specific gravity of gold compared with sand, clay, &c, but at this stage in the evolution of gold extraction we find the first move made towards a chemical method. When there was a lot of rich dirt in his pan, the digger found it very difficult to wash away the last of the sand without losing a large portion of the finelydivided gold, so he hit on the expedient of pouring in a little mercury, which formed a heavy massive though fluid alloy with the gold, making the separation of the last portions of the light granular sand a very easy matter. This plan is still in world-wide use alike by the solitary digger who lives in a lonely canyon, and by the well-organized company that "hydraulics" 1,000 tons of ' pay dirt' per day. " Let us now look at the present state of the gold industry. " Let us imagine a digger who has exhausted all the gravel and pay dirt in the canyon or gully ; he travels up the gully looking to the right hand and to the left for traces of the precious metal; occasionally he finds a piece of gold-bearing rock, and is led on and on till he finds the source of these auriferous stones to be a reef. Now begins gold-mining proper. A shaft is sunk on the reef, or a tunnel driven into it, and great masses of rock are brought to the surface, and naturally the miner is led to imitate Nature by crushing this rock to a fine sand, and then he modifies the treatment formerly given to alluvial deposits, to adapt it to the new circumstances. The ore, immediately on being crushed to powder (which is generally done by huge gravitation stamps), is carried over an amalgamated copper plate by a stream of water. In passing over the amalgamated plate the gold is caught by the mercury, while the sand, now called tailings, is washed off. The gold is recovered by scraping the amalgam off the copper plate at stated intervals, generally once a month, when by distillation the mercury is recovered as well as the gold separated. If all the gold the ore contained existed in the heavy metallic form, the recovery by this method would be complete and the loss nil; but the tailings are frequently found to contain a little gold, and on close examination particles of pyrites and sulphides of the various base metals are found diffused through the mass.