February 12, 1897.] 



SCIENCE. 



243 



in oxygen gas, as at present known and 

 worked in many laboratories, leaves very 

 little to be desired, so far as accuracy is 

 concerned, and is sufficiently rapid for most 

 commercial uses. The modification intro- 

 duced some years ago, of using a solution 

 of the double chloride of copper and am- 

 monium, instead of simple chloride of cop- 

 per,* to release the carbon from the iron, 

 took away from the combustion method one 

 of its greatest difficulties ; viz., the long time 

 required to dissolve the metal. The modi- 

 fication, as many will doubtless remember, 

 reduced the time required for solution, from 

 two or three days to an hour or less. In- 

 deed, at the present time, if a good stirring 

 machine is used, it is quite possible to dis- 

 solve three grams of fairly fine borings of 

 pig iron, wrought iron or steel, in 200 cc. 

 of the proper solvent in from ten to forty 

 minutes. 



Still further the studies of the Com- 

 mittee of International Standards for the 

 Analysis of Iron and Steel have further 

 modified tlie method, and it is believed ren- 

 dered it much more accurate. Among these 

 modifications may be mentioned the use of 

 an acid instead of a neutral or basic so- 

 lution of the double salt to dissolve the 

 metal This point was thoroughly worked 

 out by Blair.j- Following this came the 

 work done in the laboratory of the Pennsyl- 

 vania Railroad Company, J demonstrating 



* It is difficult to say positively who first suggested 

 tbis modification. The first mention in literature 

 that we are able to find is in the Transactions of Vie 

 American Institute of Mining Engineers, 4, 157, by J. 

 B. Pearse. But a private communication from An- 

 drew S. McCreath states that he made the suggestion 

 while working under Pearse, and that Professor Eich- 

 ter, in the Leoben Jahrbuch, had previously suggested 

 the use of potassium or sodium chloride with copper 

 chloride, which led him to try the ammonium salt. 

 McCreath's description of the method as used by him- 

 self is published in the Transactions of the American 

 Institute of Mining Engineers, 5, 575. 



tJVans. Am. Inst. Mining Eng., 19, 614. 



iTrans. Am. Inst. Mining Eng., 20, 242. 



the unreliability of the use of the double 

 chloride of copper and ammonia as a solvent, 

 owing, as appeared later, to the probable 

 presence in all ammonia and its salts, ob- 

 tainable in the market, even those marked 

 ' C. P.', of some carbonaceous material, pos- 

 sibly pyridine, derived from the gas liquor 

 used in making the ammonia. 



The substitution of the potassium* for 

 the ammonium salt has apparently com- 

 pletely overcome this difficulty, and this 

 with the use of oxygen gas instead of lead 

 chromate, in which to burn the carbon, and 

 some modifications of the absorbing and 

 purifying train, have seemingly placed the 

 dry combustion method for determining 

 carbon in the front rank of successful and 

 accurate analytical processes. The prin- 

 cipal known source of error in the method 

 at the present time appears to be in con- 

 nection with the weighing. The potash 

 bulbs and small calcium chloride tube used 

 in absorbing the carbon dioxide weigh, alto- 

 gether, some fifty to sixty grams, and pre- 

 sent considerable surface. If now, between 

 the weighing before the combustion and the 

 weighing after the combustion, the interval 

 being an hour, or a little more, there is con- 

 siderable change in the hygroscopic con- 

 dition of the atmosphere, an error of 0.01 

 per cent, may be easily introduced. If we 

 may trust our experience, it is difficult to 

 make closely agreeing duplicate combus- 

 tions in showery weather. Blair suggests 

 a method of overcoming this difficulty, con- 

 sisting in having a second potash bulb and 

 chloride of calcium tube of, as near as pos- 

 sible, the same size on the opposite end of 

 the balance when weighing. 



In regard to the accuracy of the method 

 as at present understood, it may be said 

 that, undoubtedly, the best test of the accu- 

 racy of a method is the recovery of a known 

 amount of any substance added to the ma- 

 terial to be analyzed. This procedure 



*J. Am. Chem. Soc, 15, 448. 



