SAMPLING. The first operation in making an assay is to select the sample. This work should he fairly done. no discrimination against any portion of the lot from which the sample is taken being allowable. There are two kinds of sam pling: (1) ore sampling, and (3) sampling of metallurgical products. There are various methods of taking a sample of ore, it being done both by hand and by machine. (Me form of hand sampling only will he described here, whieb is generally termed quartering. This method is as follows: As the ore-ea•s are Un loaded every tenth shovelful taken indis•rimi nately is thrown into a wheelbarrow IS a sample. When about ten tons have thus been selected. it is shoveled into a conical heap, which is then flattened out into a circular cake and divided diametrically into quarters, as one would cut a pie. Two opposite quarters are then thrown aside, and the other two made into a second cone, which is flattened and quartered as before, two quarters being thrown aside and two shoveled into a third cone. This process is repeated, the ore being occasionally crushed smaller as the amount decreases, until the samples here remain ing are a mass of powder, weighing from one to three pounds. This is ground until it will pass
through a very fine sieve, and is spread out and tilled into two sample bottles by taking por tions here and there on the point of a steel spat ula. In sampling metallurgical products. drill ings are taken from the bars of metal, or the hot metal may be ladled directly from the fur nace.
When an assayer receives a sample for deter mination, he proceeds first with a preliminary examination by means of microscopical studies and blowpipe tests to familiarize himself with the general character and etimposition of the substance. The formal analysis is then under taken. The laboratory apparatus necessary for genera] assaying is quite extensive, consisting of a large variety of chemicals, balances, crueibles, eupels, furnaces, beakers, etc. A different mode of procedure is adopted in assaying differ ent metals, and for illustration the method of assaying gold and silver by the fire-assay, and of silver by gravimetric analysis, will be described, the reader being referred to special treatises on assaying. metallurgy, and chemistry for details of the processes employed for other metals.