Mohave County miner., 1884-01-13
Preparation of Ore for Assay.

sample need be so. A large sample
 is broken by hammer and block
 pestle and mortar, etc, so that DC
 one piece shall be a considerable
 fraction, say more than one-thous-
 andth of the whole, then mixed on a suitable cloth or smooth table. The sample is then spread in layer, and divided, by the back of saw-blade,
 trowel, or spatula, into quar- ters
 Two opposite quarters are rejected
 and again mixed, after further pul
 verifying. if needful and again divid- ed. When reduced to pound or so the sample is passed through the coarser sieve, and now sheet of strong paper or Oilcloth is suitable to mix on, by lifting an edge and drawing 1t forward so as to roll the sample upon itself, and to heap it Tn the middle; then agaln spreading by the spatula, and so several times. The sample is thus gradually reduced in quantity, being more finely ground step by step, until several ounces have passed through tue finest sieve.
 For mixing sample, after 1t has reached a certain fneness, no Im- plement Is equal to the finger. Heap the ore, then, with the finger, begin ming at the center of the heap, trace a spiral to the edge and back to the center. Again heap by lifting the edges of the sheet, and again spread by the finger, and so on.
 Without perfect mixture at each stage of division, the final sample will not be true one, ard this final sample must again be mixed, in or der that each assay taken from it may also be true sample of the whole. AHides. et what is required may be got by adding a little flour to finely powdered samplG of dark colored ore, or charcoal to light colored one. and mixing until the tint Is uniform without streaRs CT spots.
 Each time that a sample $ ground or sifted the wh&e of it must pass AtthrougA 8 sie unless there are  particles of tough matter, such as metal, or silver-glance. etc, which cannot be ground to a powder. 4n this case the tough matter must be kept, and no further division of the sample can be made, as it must all be weighed and treated as directed further on.
 Damp ore must be dried. In par ticular cases all samples, whether they appear damp or not, should be dried after being powdered, then al lowed to cool before weighing the assay. Many substances, such as clay, for instance, lose more and more water at successive degrees of heat up to whiteness, wherefore there must be standard temperature for the drying. That standard Is the heat of boi ling water; hence the sample is dried on the water bath.
 All implements used in powdering and sitting must be cleaned, lest the sample be contaminated by some re- mains of a former one. In many cases simply wiping the mortar, etc., with cloth will suffice, but after rich ore, the tools must be cleaned i by grinding some barren quartz, sand, or glass. Sieves are cleaned i by brushing and tapping.
 The prepared sample is put in sample pan with tag on which is marked the number of the sample, and any desired particulars, such as the general character of the ore, as guide in dressing or the metal for which It is to be assayed, etc.
 The character of the ore can, in general, be ascertained sufficiently and most conveniently by an exam ination of it in the lump before grind ing. When this cannot be done, as in the case of samples which come already ground, recourse must be had to washing. (panning) little of the powder in dish, by which the character and proportion of sulphur cts may be judged, ii there are any The color and general appearance also furnish indications, or special tests may be applied, some of which are given further on.-Mining and Scientific Press.
 D.~oLoHAI Al