advantage of and the decision of the Board of Appraises and in some cases of the secretary of the Treasury is final. These decisions are printed in a series entitled Treasury Decisions and published by the Government, the decisions being numbered consecutively. This series is hereinafter cited T. D., and an abstract is given of the most important decision directly concerning minerals. Articles of jade (vases, etc.) are dutiable as articles composed of mineral substances and not as precious stones.* Ground talc or French chalk is dutiable as a mineral substance (p. 97, act '97).† Sapphire meter jewels or compass centers are classified as mineral substances at 25 per cent. ad valorem (p. 97, act '97) and not as precious stones. Imitation pumice stone and scouring bricks are dutiable as mineral substance. § Molybdenite is dutiable as a metallic mineral substance. || "Putz pomade" is dutiable as an article composed wholly or in chief part of mineral substance. T Gravel bought as ballast is entitled to free entry and crude mineral. ** Caen stone sweepings from a marble or a stone yard are free as crude mineral.†† Lime rock (rubble) is entitled to free entry as an unenumerated crude mineral.++ Articles made of "tiger-eye" is classified as a mineral and not as a precious stone. §§ Artificial teeth are dutiable as articles of mineral substance under par, 97, act of '97. I Electric light carbons are classified as "mineral substance." Actinolite is dutiable at twenty per cent. ad valorem and is not the same as asbestos.* Apatite is free under the act of 1895, p. 500, for use as manure.† Siliceous stone is a mineral substance and when ground is "advanced in value or condition" and dutiable, and not free as sand.‡ Cornish stone was found to be a variety of feldspar and held not dutiable, being a crude mineral.§ Talc is non-dutiable as a crude mineral and does not come under the classification of French chalk.|| Earth composed of oxide of iron, silica, alumina, and lime used as a polishing powder is dutiable as an "earth manufactured" at $3.00 per ton.¶ Asphaltum is non-dutiable coming under the classification of a crude mineral.** Under the last subdivision of this subject no further summary is possible than the enumeration and digest of the decisions given. herein; for each decision being the interpretation by a court or other proper authority as to what is included under the term. mineral, mineral load, crude mineral, etc., as used in the statutes cited, the case of each particular substance must be decided by the facts relating to such substance so that the precedent of the case does not go farther than the substance passed upon or those so similar as to be practically identical. It may be noted, however, that in all the subdivisions of the subject that the cases show an increasing tendency of the courts and other authorities to call for and rely on the expert testimony of scientific men, - chemists, engineers and geologists for aid in deciding the important cases that arise under this subject. As the quotations given above from the early cases indicate, there then existed a marked tendency in the courts to make some supposed understanding of the "mass of mankind" the basis of decisions on these questions, usually with unsatisfactory results, while those decisions arrived at by the aid of competent scientific testimony have stood and become reliable. precedents. *T. D. 16,013. T. D. 15,701 (1895). T. D. 10,784. **T. D. 12,817. THE EFFECT OF VARIATIONS IN THE SPEED OF CRUSHING MACHINERY UPON THE PRODUCTION OF UNDERSIZED MATERIAL.* BY H. W. GARTRELL. The proper speed at which a crusher should be run is of obvious importance, since it directly governs the output, and large output being one of the chief objects in many mills there is a tendency to run crushers at higher speeds than formerly. This is especially the case with rolls, the speed of the old Cornish rolls having been multiplied many times in modern design. Various points however need consideration, for instance one mill in this country changed the speed of a pair of rolls from 102 to 92 revolutions, to overcome excessive wear of the cast steel faces, while another in crushing a limestone galena changed from 35 to 28 revolutions to prevent glazing. The object of this investigation was to follow up another line, that of the production of undersized material, which is responsible for so large a proportion of the losses of many mills. There seems to be a general impression that high speeds give an undue proportion of such material, though the authorities are almost entirely silent on the subject. The writer has not been able to find any published investigations on this point, though he believes that in the case of coal crushing by toothed rolls, some unpublished tests fully confirm the idea. In the case of ores it is not sufficient to know the amount of undersized material produced, but also to gain some idea of the effect on the economic minerals present, for it is in these that the losses occur. A tough galena-blende ore was selected, the gangue being siliceous with large quantities of feldspar, and an attempt was made to judge the effect on the galena by vanning the material passing a 16 mm. screen. The results, however, were so irregular that a second investigation was conducted on a sample of carefully cobbed galena, which from the very high proportion of brittle mineral would show any variations of importance. The machines used were a Krom jaw crusher, 5" by 12", of the type shown on p. 32 of the catalogue of '97 to '98; a style F, third pattern, Gates crusher and a pair of 16" Krom Rolls designed to run at 100 and 101 revolutions. Of * Submitted in partial fulfillment of major subject for degree of Master of Arts, in the School of Mines, Columbia University. these the gyratory is naturally very much smaller than would be used in practice, but the other machines are large enough for commercial use. The products were screened in a series of screens approximating Rittinger's scale, and ranging from 44 mm. to .16 mm., the work being done wet below 2.5 mm. All the holes were square and the measurements given are the mean linear apertures. After the coarser sizes had been removed a split sampler and riffles were used to diminish the quantity handled, the principle observed being that the aperture of the sampler should be at least four times. the diameter of the largest particle. The speeds of jaw crusher used ranged from 73 to 520 revolutions per minute for the ore, and 70 to 537 revolutions for the galena. As American practice, Richards quotes 59 breakers of the Blake type ranging from 84 to 500 revolutions with a mean of 252. It may be noted that only one machine, a 6" by 8", ran at 500 revolutions, and two, an 8" by 10" and a 6" by 9" at 400 revolutions, suggesting that the reason for these exceptional speeds was a necessity for maximum capacity. Five breakers of the Dodge type ranged from 190 to 366 revolutions, with a mean of 254. For spindlebreakers the same authority quotes pulley revolutions of 320 to 500 with a mean of 402, and catalogue speeds of 350 to 700, the last figure however being for a laboratory crusher. In these SCREEN-CLASSIFICATION OF ORE CRUSHED IN JAW CRUSHER. .51 .8 .7 .16 <.16 .6 96.8 96.6 1.5 1.5 1.4 1.2 98.3 98.1 98.3 1.7 1.9 1.7 1.4 100.0 100.0 100.0 100.0 354 248 297 284 Weight of ore in pounds. 284 354 248 297 .8 .7 96.0 95.9 96.2 96.8 .7 96.9 97.4 98.6 experiments the extremes were 1 36 and 980 revolutions and 141 and 1,004 for ore and galena respectively. Finally 71 rolls are quoted as ranging from 8.5 to 130 revolutions with a mean of 53, though recent catalogues give 50 to 180, while 20 to 145 and 20 to 143 were the limits used here. SCREEN-CLASSIFICATION OF ORE CRUSHED IN GYRATORY CRUSHER. This series of experiments then may be taken as including all normal practice, and in most cases reaching well beyond the limits. |