POPULAR MISCELLANY. 



427 



uct of American corundum was six hun- 

 dred and forty-five tons. Unlike corundum, 

 emery consolidates in large masses. It 

 does not, indeed, form continuous beds of 

 great extent, but its discontinuous masses 

 and .veins sometimes contain hundreds of 

 tons. The emery-bearing locality in West- 

 chester County, New York, is a strip from 

 one half to three fourths of a mile in width 

 and from five to six miles in length. The 

 place in which the largest openings have 

 been made, and which has excited the most 

 interest, is on a part of a summit about 

 three miles from Peekskill and seven hun- 

 dred or eight hundred feet above tide level. 

 It overlooks, on the one side, the valley of 

 the Croton, whose stream is invisible, and, 

 on the other side, the Hudson. On the 

 north and northeast of the emery belt are 

 outcrops of granite. South of it lies the 

 common marble of Sing Sing; still farther 

 south, at Spuyten Duyvil, occur the oldest 

 of the Laurentian gneisses ; and still farther 

 south, on Manhattan Island, the mica schist. 

 The emery is, however, all immediately as- 

 sociated with a hornblende rock. Large 

 masses of emery are seen projecting above 

 the surface. These are delusive, and those 

 which hold out a large promise are some- 

 times found to extend only one or two feet 

 underground and to yield only from five to 

 twenty tons. Such masses are usually sur- 

 rounded by soft, reddish earth. 



Substitutes for White Lead. Only two 

 substances at present manufactured are re- 

 garded by Mr. A. P. Laurie as satisfactory 

 substitutes for white lead in painting sul- 

 phate of lead and oxide of zinc. Sulphate 

 of barium has hardly any covering power, 

 and sulphide of zinc, though remarkable for 

 covering power, has not proved, as at pres- 

 ent manufactured, a durable pigment. Ox- 

 ide of zinc, though deficient in covering 

 power, is remarkably white, and preserves 

 its color in impure air. Sulphate of lead is 

 in the market in two forms sublimed sul- 

 phate, which is prepared directly from 

 galena ; and precipitated sulphate, ground 

 by Freeman's patent with oxide of zinc, and 

 sold as Freeman's white. Sulphate of lead 

 prepared by sublimation has much more 

 covering power and is much denser than 

 precipitated sulphate. Another pigment 



sold as a harmless white lead is prepared 

 in a similar way by grinding together oxide 

 of zinc and sulphate of barium. In quan- 

 tity of oil required the substitutes named 

 compare well with white lead, some taking a 

 little more and some a little less, except 

 oxide of zinc, which takes a very large 

 quantity. In the matter of susceptibility to 

 impure air, they all have a distinct advan- 

 tage over white lead. Zinc oxide is not at 

 all affected, and the sulphate is very slightly 

 affected unless the gas is in very large quan- 

 tities and the paint is wet. In durability 

 under outdoor exposure they are not better 

 than white lead, except that oxide of zinc 

 remains white. In their appearance in oil 

 they differ considerably from white lead, 

 being thin and stringy instead of stiff and 

 firm, and this is against them. But Mr. 

 Laurie does not find that when thinned 

 down they seem to differ appreciably from 

 lead carbonate in ease of w y orking. In their 

 effects on health, oxide of zinc is harmless. 

 Sulphate of lead is not absolutely insoluble 

 in very weak hydrochloric acid, and may 

 therefore be slightly soluble in the stomach 

 and to some extent poisonous ; but the au- 

 thor does not believe that under ordinary 

 conditions of manufacture or use it would 

 produce lead poisoning. 



The Dangerous Proportion of Carbonic 

 Acid. Of the power of carbonic acid to 

 smother, Prof. F. Clowes, of Nottingham, 

 England, ascertained that the flames of can- 

 dles, oil, paraffin, and alcohol are extinguished 

 by air containing from thirteen to sixteen 

 per cent of carbonic acid. The flame of 

 coal gas requires the presence of at least 

 thirty-three per cent of the extinguishing gas, 

 while the flame of hydrogen requires fifty- 

 eight per cent. Concerning the proportion 

 of carbonic acid mixed with water that can 

 be breathed with impunity, the statements 

 of different observers are conflicting. Prof. 

 Clowes finds ten per cent more than is required 

 to extinguish a candle flame respirable, while 

 Dr. Haldane, of Oxford, estimates that air con- 

 taining twenty per cent of carbonic acid can 

 not be breathed, even for a minute, without 

 serious consequences ; even five per cent, he 

 claims, caused serious distress of body and 

 mind, while any proportion higher than ten 

 per cent produced distinct poisonous effects. 



