195 



sisted in using a jar or pitcher, rather larger than the specimen, and 

 not over-large at the mouth ; this was filled with water up to 

 a marked line; and then, by introducing the specimen, and bringing 

 back the water to the same line, so much water was removed as was 

 just equal in bulk to the bulk of the specimen ; the weight of this wa- 

 ter gave the divisor, the weight of the specimen (taken while dry), the 

 dividend, and the quotient was the specific gravity. 



The results thus obtained were, generally, as satisfactory as those 

 by the usual method. And here it may be interesting to cite a few 

 examples, from our minutes, of specimens estimated by one or other 

 of the processes mentioned, and afterwards melted down and assayed 

 as regular deposits. 



1. A lump of quartz, containing gold, found by two Mexicans of 

 the "Sonorian camp," in California, weighed 2651 ounces; assuming 

 the quartz at the sp. gr. of 2.60, the amount of gold appeared by sp. 

 gr. of the lump, to be 209^ ounces; the actual amount was 211-i 

 ounces. — 2. Another lump, where we assumed the matrix at 2.64, 

 gave an estimate of 100^ ounces of gold ; the actual product was lOOJg- 

 ounces. — 3. Four pebbles taken together, estimated at 77 ounces; 

 actual content, 76y^^ ounces. — And, lastly, a lump which had been 

 bought in California for 800 dollars, and which weighed 408^ ounces, 

 gave an estimate of 891 ounces, or 1572 dollars, taking the matrix 

 at 2.63; the actual yield was 91y^o ounces, or 1602 dollars; the fine- 

 ness beino; 850 thousandths. In this case there was an error of 30 

 dollars, or about two percent, upon the value; an amount of error to 

 which such specimens are liable, with any apparatus. 



But it was obvious that the method of displacement required a se- 

 ries of vessels, specially adapted to the operation, to compete with 

 weighing, in closeness of results. After a good deal of reflection, 

 and experimenting, in which many modifications of shape and arrange- 

 ment were tried and discarded, and which it would be cumbersome 

 to notice in this place, the apparatus now shown was found to answer 

 best. In practice, it is really a pleasant and satisfactory substitute 

 for the tedious and irksome method usually resorted to. Some fe\v 

 precautions must, of course, be attended to. The vessel must stand 

 firmly. If at first the water will not flow, or flows fitfully, the ob- 

 struction will be removed by blowing a little in the spout. 



An investigation of some interest, growing out of this matter, may 

 properly be noticed. Where we are operating upon substances of 

 low specific gravity, say wood or stone, a drop or two of water, or 



