302 ANNUAL OF SCIENTIFIC DISCOVERY. 



due its value in the arts. The method adopted by Dr. Smith for de- 

 termining the hardness of different varieties is by observing the abra- 

 sion caused by the rubbing of a definite amount of emery upon the 

 surface of glass with the bottom of an agate mortar, the abrasion 

 caused by pulverized sapphire being taken as a unit of comparison. 

 By this method the best emery is found capable of wearing away about 

 one half of its weight of common French window-glass, the sapphire 

 under the same circumstances wearing away four-fifths of its weight. 

 In its chemical composition, emery consists of alumina, from 60 to 77 

 per cent. ; oxide of iron, from 8 to 33 per cent. ; lime, from 0.40 to 

 2.80 per cent. ; silica, from 1.80 to 9.63 per cent. 



The mining of emery is of the simplest character. The natural 

 decomposition of the contiguous rock facilitates its extraction in blocks 

 and large masses, which are afterwards broken by hammers into a con- 

 venient size for transportation by camels or horses. In some localities 

 the mining is attended with great difficulty, as the tools used for boring 

 are rendered unfit for use by coming in contact with pieces of emery. 

 The annual consumption of emery at present, is about fifteen hundred 

 tons. The price at the end of the last century was from 40 to 50 dol- 

 lars per ton, and between 1820 and 1835 it was at times even less. 

 About this period, the monopoly of emery in the island of Naxos was 

 purchased from the Greek government by an English merchant, who 

 so regulated the quantity given to commerce that the price gradually 

 rose from 40 to 140 dollars the ton, a price at which it was sold in 

 1846. Since then, the emery mines discovered by Dr. Smith in Asia 

 Minor have been so successfully worked, under the auspices of the 

 Turkish government, that the price has now diminished to 50 and 70 

 dollars per ton, according to the quality. 



ON RUTILE AND CHLORITE IN QUARTZ. 



SPECIMENS of rutile in quartz have for twenty years past been found 

 in boulders in several towns in the vicinity of Dartmouth College, 

 none of which have ever been traced to their sources. Localities have 

 been mentioned, but none have furnished specimens resembling these 

 boulders, excepting a single one. This locality was opened two years 

 since at Waterbury, on the Central Railroad. In a cut of sixty feet 

 depth through solid talcose slate, and thirty feet from the surface, a 

 vein of quartz was met, and a considerable number of specimens con- 

 taining rutile were obtained. The locality is now exhausted, and 

 fiom its position could not have furnished the scattered masses hereto- 

 fore known. Some of the specimens from this region are exceedingly 

 beautiful, both in the richness of the quartz and the abundant long 

 needles of the rutile. The rutile crystals are from the size of the finest 

 hair, so as to be almost invisible, up to the twelfth of an inch in diam- 

 eter and five inches long ; they are uniformly distributed throughout 

 the quartz, and intersect and cross each other in all directions. There 

 is no radiation from a centre, but in many instances the crystals have 

 one or more large, graceful curves, and sometimes two in opposite di- 

 rections, and some are bent at an angle either right or oblique. Many 



