Quantitative analysis in practice Author:John Waddell 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 GENERAL DIRECTIONS REGARDING WORK 1. TIDINESS.—For the purposes of both accuracy and speed, tidiness is very important. The work table shoul... more »d be kept scrupulously clean, the bottles containing acid and ammonia, which are in constant use, should be washed off at the beginning of each laboratory period, since, on standing for even a few hours, they become coated with ammonium salts, formed from the fumes of the laboratory or from the contents of the bottles themselves. Round the stopper distilled water should be poured. The lip should not be wiped off with a towel on account of lint or other dirt. Bottles used only occasionally should be similarly washed before pouring out the reagent. No stopper of a bottle should be placed upon the table or held within the fingers in such a way that the part entering the neck of the bottle will be touched. Before a cork is removed from a bottle containing a solid, the dust must be carefully wiped from the edge with a very clean cloth or filter paper, and, of course, the cork must not be laid with its underside upon the table or any place where it could get the smallest particle of dust. It is best to lay it upon its upper side. At the end of the laboratory attendance the desk should be left perfectly tidy; no burettes, water baths, or other apparatus should be left upon it. 2. REAGENTS.—Each student is responsible for the purity of the reagents which he uses. A reagent which looks cloudy should never be used without filtering, no matter how many have been taking from the same bottle. Reagents should be tested from time to time for possible impurities that might be injurious, such as silica in ammonia, or chlorides and sulphates, when these are to be determined, or would in any way vitiate the results. It need hardly be s...« less