November 24, 1893.] 



SCIENeE 



283 



SCIENCE: 



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CURRENT NOTES ON CHEMISTRY.— TV. 



{Edited by Charles Piatt, Ph.D., F. C. S.) 

 Advance in the Analytical Chemistry of Recent Years. 



Pkof. Albert B. Phkscott has outlined some of the most 

 distinctive advances of analytical chemistry in a paper 

 read before the "World's Congress of Chemists. First we 

 have "the resolute attempt to find out the composition of 

 matter, as a whole, in any and all of its mixtures of what- 

 ever source." Complete analysis, proximate and ultimate, 

 of complex substances has been entered upon, and "unde- 

 termined residues" have been made the beginning instead 

 of the end of chemical research. The courage of analytical 

 effort in recent years has been seen especially in the 

 elaboration of methods for the isolation of carbon com- 

 poirnds, both natural and artificial. Proximate organic 

 analysis has been called for by many practical workers, 

 and we are now enriched by the labors of thousands in 

 this field, which was opened largely by Dragendorif and 

 Hoppe-Seyler. We have an increased knowledge of the 

 molecular structure of bodies produced by nature — mineral, 

 vegetable, and animal, as well as those of artificial produc- 

 tion. Important advance has also been made in the em- 

 ployment of physical methods of inspection whereby mole- 

 cular change is avoided. We have but to mention in this 

 connection the multiplication of optical methods, the 

 polarimeter, the refractometer, the sj)ectroscope, recent 

 studies in molecular mass, the freezing and melting points, 

 solutions, adhesion and capillarity. 



An exhibition of advance made is furthermore found in 

 the reciprocal benefits of scientific research and of tech- 

 nical skill as seen in the work of experts in biological and 

 pathological analysis, sanitary and forensic analysis, in 

 the industries, and in agriculture and metallurgy. 



Sodium Peroxide in Analysis. 



Probably no other recent addition to the reagents of 

 the laboratory has become of such importance as has the 

 peroxide of sodium, Na^ O,. Its suf)eriority as an oxidizing 

 agent is firmly established, both because of its purity and 

 because of its rapiditj- of action; and while but a few years 

 ago it w;is something of a curiosity, it is now an article of 

 commerce used in industrial operations, as well as in the 

 finer applications of the laboratory. So long ago as 1871 

 Dr. John Clark pointed out, through the Chemical Neivs, 

 the strong oxidizing power of a mixture of caustic soda 

 and calcined magnesia, and, a little later, illustrated the 



value of this action in the analysis of sulphides. As Dr. 

 Clark states in a recent paper in the Journal of the Chem- 

 ical Society (London), the exact cause of the above action 

 was not quite clear at the time, but has since been de- 

 termined by him to be due to the formation of the perox- 

 ides of sodium and magnesium. Hempel shows the supe- 

 riority of the peroxide for the detection of chromium and 

 manganese, and for rendering titaniferous iron ore soluble, 

 but considers that for the oxidation of sulphur compounds 

 that the addition of sodium carbonate is necessary to re- 

 duce the violence of the action. Clark, however, in the 

 article referred to, prefers to use the peroxide without ad- 

 mixture with carbonate, stating that when a sufliciently 

 low temperature is employed there is less tendency to loss 

 by sjjurtiug and the action is completed in less time. In 

 the analysis of pyrites, the procedure is as follows: One 

 part, by weight, of the pyrites is mixed with six parts, by 

 weight, of sodium peroxide in a platinum or nickel crucible, 

 placed about two inches above a very low Bunsen flame. 

 Oxidation immediately sets in and the mixture becomes 

 red-hot. A few minutes suffices for the action, and upon 

 its completion the sulphur is easily soluble in water. The 

 solution is acidified and the sulphur precipitated as 

 barium suljDhate. In the case of blende part of the zinc 

 dissolves with the sulphur, so that when it is desired to 

 determine the zinc also the mixture is acidified with 

 hydrochloric acid and precipitated with sodium carbonate 

 before filtration. Galena, after treatment with peroxide, 

 yields part of its lead into solution, and it is therefore 

 advisable to acidify slightly with nitric acid and to boil 

 with excess of sodium carbonate, when all the lead will be 

 rendered insoluble, and upon filtration the whole of the 

 sulphur will be found in the filtrate. By fusion with 

 jDeroxide, arsenic is converted into soluble arsenate, and 

 may then be estimated by any of the ordinary .methods. 



Dr. Clark uses peroxide of sodium most advantageously 

 in the estimation pf chromium and in the analysis of 

 chrome ore. The temperature should not be so high as to 

 liquefy the mixture, but just enough to form a paste, under 

 which condition the contents of the crucible shrink, leav- 

 ing a space between the mixture and the walls of the 

 crucible. The mass is extracted with water and the solu- 

 tion boiled to decompose any excess of peroxide if the 

 chromium is to be titrated. The insoluble residue dis- 

 solves easily in hj'drochloric acid, and should be tested 

 for any traces of undecomposed ore. The beauty and ease 

 of this p)rocess can only be fully realized by analysts who 

 have had practical experience with refractory chromium 

 compounds. The analysis of ferro-chromium is conducted 

 in the same manner, the metal being first reduced to. a 

 fine powder and then mixed with six times its weight of 

 peroxide. This reagent is also applicable with some mod- 

 ifications in procedure to the quantitative estimation of 

 chromium in steel, and in the quantitative separation of 

 manganese from zinc, nickel and cobalt, the solution in 

 this latter case being made in cold water, to avoid de- 

 composition, which gradually sets in. In the separation 

 of zinc and manganese, the latter is thrown down perfectly 

 free from the former by the addition of peroxide to the 

 ammoniacal liquid, or, as is recommended in the separa- 

 tion of manganese and cobalt, that the cobalt should be 

 in the highest state of oxidation, the sodium peroxide may 

 be added to the cold acid solution before rendering it 

 alkaline with ammonia. In the separation of manganese 

 from nickel and cobalt it is advisable to redissolve and to 

 repeat the operation. Another valuable apislication of 

 sodium peroxide is in the breaking down of tungsten 

 minerals for analj'sis. 



In a paper read before the British Association, at the 

 Nottingham meeting. Dr. S. Rideal and Mr. H. J. Bult 



