282 MACHINERY IN THE TRANSVAAL. 



for the Kimberley Imperial Mine at Barberton, but which was 

 stopped at the Rand whilst en route to Barberton j the 30-stamp 

 mill for the Paarl Pretoria G.M. Company, and the lo-stamp mill 

 for the Langlaagte United. These mills were all of 8501b. stamps, 

 and the two first-named had Corliss engines and return tubular 

 under-fired boilers. The smaller mill was driven by a slide valve 

 engine, with a return tabular under-fired boiler. They were sup- 

 plied with Blake ore crushers, and were noticeable as being the 

 first mills equipped with Frue vanner concentrators, which for a 

 considerable period was regarded as the standard machine for 

 this purpose on the fields, until the extended developments of the 

 cyanide process demonstrated that close concentration was neither 

 necessary nor desirable. Just about this period, the writer became 

 an advocate of condensing being applied to the mill engines, as 

 the quantity of water required for the plates is the amount needed 

 for surface condensation of the steam required to drive the stamps. 

 I met with the most cordial support from Mr. Hennen Jennings 

 in this connection, and when the Robinson Company decided in 

 1890 to lay down a large compressor and rock drills, a surface 

 condenser was supplied for use with this plant. Attention was 

 now being turned to these American mills, and when the Lang- 

 laagte Estate Company ordered 60 stamps for their mine, and 

 the Robinson Company 40 stamps for theirs in 1888, and their 

 subsequent behaviour was satisfactory, the Sandycroft people 

 found they had a formidable competitor in the field, and orders 

 began to be more equally distributed between these two firms at 

 this time. These two mills were singular in being the first gravi- 

 tation quartz mills erected on the Rand, the ore going from the 

 mine into the top of the mill above the crusher floors and bins, 

 and gravitating through, until finally it left the launders as pulp. 

 It then went to waste on the tailings dumps, as little attention 

 was then given to these residues. About this time the Corliss 

 engine became popular on account of its speedy running under 

 variable loads, and many mills were operated with them, nearly 

 all the American-built mills being so fitted. All these engines 

 were single cylinder non-condensing, the exhaust steam being 

 utilised to heat the feed water. At this time the loco, type of 

 boiler began to go out of fashion, the larger powers demanded 

 rendering this type unsuitable for transport on wagons, whereas 

 the return tabular boiler, befing a plain cylinder, was easily 

 handled, and even if transport riders were compelled to off-load 

 on the road when stuck in bad places, it was an easy matter to 

 parbuckle one of these boilers back on to the wagon. 



The return tubular boiler did not call for a very high quality 

 of bricks for its seating, which was another advantage, and more- 

 over the grate could be made of large area, which was necessary 

 for the very inferior fuel used in those days. The bricks then 

 made were of the class known as " slope," and were hand-made 

 and burnt in clamps with wood for fuel. They were fairly cheap, 

 if not of very good quality. The size of boiler of this type then 

 generally used was 5410. diameter by i6ft. oin. long, capable of 

 developing from 80 to 90 H.P. , and the steam pressure was 80 lbs. 

 maximum. As the fields progressed, larger boilers were used 



