A Manual of Practical Assaying

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III. PRELIMINARY EXAMINATION. ALL material submitted to the assayer for analysis should first undergo a preliminary examination, to determine its character and principal constituents. A little time spent in this manner will frequently result in a great saving of time in the -subsequent analysis. If the character of the material is not understood a wrong method of analysis may be adopted, or a substance may be analyzed for some constituent which is present in such small quantities that its determination is unnecessary. Sometimes this preliminary examination is unnecessary, as when a substance for analysis is submitted with a statement of its character and the constituents required to be determined. It frequently happens that the assayer receives a substance with the request that its chief constituents be determined, in which case a few qualitative tests will generally be a sufficient guide. In the case of an ore in lump form, the assayer will be able to determine its chief constituents by an eye examination and, possibly, a few tests with the blowpipe. In 'most of our metallurgical works the assayer generally receives the sample for assay already pulverized. In this case the chief constituents and the character of the material can generally be determined readily by treating the sample as follows: Place about half a gramme of the sample on a large watch-glass, and van with a little water, by rotating and gently tapping the edge of the glass, so as to separate the lighter from the heavier particles. After thus separating the particles, an examination with the aid of a magnifying-glass will show the principal mineral constituents and their approximate amounts. The author has found this an invaluable aid indetermining what the sample should be analyzed for, and also the...