60 H. J. Grayson: 



A quantity (usually about 3 lbs.) of the finest flour emery was 

 tied up in a j^iece of linen or canvas of moderately open texture and 

 kneaded under water, preferably warm, in any convenient vessel 

 until the whole of it had been washed out. This treatment ensures 

 a thorough wetting of all the emery and prevents it from floating 

 upon the surface of the water used in the later stages of its separa- 

 tion. The water and emery were next thoroughly agitated and 

 passed tlirough a fine sieve of wire or milling silk to separate out 

 any coarse grains of emery or other material present. For this 

 and the subsequent operations, four or five large tins holding about 

 four gallons each (empty kerosene or petrol tins do very well) are 

 required. Having washed the whole of the material through a 

 suitable sieve, more water may be poured in to nearly fill up the 

 tin, to which is added a few c.c. of a 20 per cent, solution of 

 Tannic acid, Avhich acts as a deflocculent if not in excess. (Re- 

 peated additions of this solution are made with each fresh supply of 

 water as the separation process is continued). After a thorough 

 stirring, allow the vessel to stand for ten minutes and then decant 

 with care the upper three-fourths of the water, carrying in suspen- 

 sion the finer emery, into another tin. This process should be 

 repeated several times, with fresh supplies of water, until it is seen 

 that most of the finer material has been decanted from the original 

 sample. The sediment remaining will consist mainly of the coarsest 

 grains present in the original samples, and may be set aside to 

 settle in a smaller vessel or beaker and afterwards dried off. We 

 have next to deal with some 8 or 10 gallons or more of water, con- 

 taining finer emery than will fall through the depth of water each 

 vessel contains — say 8 to 10 inches in 10 minutes; but will settle in 

 say 20 minutes. Hence we proceed with the separation of this finer 

 material much in the same way as we dealt with that which came 

 down in 10 minutes, providing sufficient vessels are available; if 

 not, allow the vessels containing it to stand and settle for about 

 SO minutes, when the upper portion of tlie water in each, in which 

 tliere will remain in suspension only fine material of little or no 

 abrasive value upon a screAv, may be poured away as close to, but 

 without disturbing the sediment, as possible. The several sediments 

 having been transferred to one vessel, with additional water as 

 required, and well stirred, are allowed to stand for 20 minutes, 

 Avhen the upper portion of the Avater containing still finer emery is 

 poured off, as l)efore, into other tins. The addition of fresh sup- 

 plies of water and time for settlement (20 minutes) being continued, 



