138 



CHEMISTRY. (CHEMICAL ANALYSIS.) 



the atomic weight of osmium, by which the true 

 value of the constant is fixed at 190*3 and it given 

 a place at the head of the platinum group in- 

 stead of at the end of it. 



In his new system of atomic weights, founded 

 in part on the direct determination of the mo- 

 lecular weights, A. Leduc has found the atomic 

 weight of oxygen the density of the gas with 

 reference to air being 1-10503, and that of nitro- 

 gen 0-97203 to be 15 '88. He has more recently 

 determined the molecular volume of carbon 

 monoxide, with reference to oxygen under nor- 

 mal conditions, to be close upon 1-0001. Hence 

 we are led to admit that nitrogen and carbon 

 monoxide, by reason of the proximity of their 

 critical points, have, to within about r^Tm part, 

 the same molecular volume. The atomic weight 

 of nitrogen is hence deduced as 13-97, while the 

 determinations of Stas lead to the value 13-94 ; 

 that of silver as 107-17 ; that of chlorine as 

 35-21 ; that of bromine as 79-39 ; that of iodine as 

 125-96; and that of carbon as 11-916. 



As the result of eleven series of experiments 

 embodying 43 determinations, Theodore W. Rich- 

 ards computes the atomic weight of copper 0= 

 15-96 as 63-44; O=15'87 as 63-09. In his in- 

 vestigation every reaction was assumed to in- 

 volve some constant error, and every substance 

 to contain some constant impurity, till the con- 

 trary was proved. 



Chemical Analysis. An account of an in- 

 vestigation of the composition and properties of 

 the dangerous explosive iodide of nitrogen has 

 been published by Dr. Szuhay, of the University 

 of Buda-Pesth. The substance was obtained by 

 adding excess of aqueous ammonia to a concen- 

 trated solution of iodine in potassium iodide in 

 the form of a very fine powder, which was found 

 to be capable of safe purification by washing 

 with a dilute solution of sodium sulphate. -The 

 filter should be protected from draughts of air, 

 which are liable to induce explosion. The puri- 

 fied substance in a moist condition, because it 

 can not be dried without explosion was analyzed 

 by decomposition with a solution of sulphurous 

 acid of known strength, and estimation of the 

 amount of iodine and ammonia in the solution. 

 Its composition was proved to be NHIj, as Dr. 

 Gladstone and Bineau had determined it. This 

 conclusion as to its composition is also supported 

 by the fact that Dr. Szuhay has been able to 

 prepare a silver derivative of the compound by 

 replacing the hydrogen atom with silver. The 

 silver compound is a black flocculent substance, 

 quite as explosive as iodide of nitrogen itself. 

 When it is carefully dried, the least rise of tem- 

 perature provokes explosion. It also detonates 

 on being struck, or even when brought into 

 gentle friction with any other substance. When 

 warmed under water, or when treated with dilute 

 acids, it is quietly decomposed. Evidence was 

 adduced by the author to show that potassium, 

 sodium, and barium replacement compounds are 

 capable of existence in solution. 



A comparison of the results given in the 

 "School of Mines Quarterly" by Dr. Waller, of 

 Columbia College, of his recent determinations 

 of the dissolved salts in the water of the Great 

 Salt lake with those obtained by Gale, Allen, 

 Bassett, and others, shows that the salinity is 

 constantly changing ; and a closer examination 



reveals the fact that there is a variation from 

 place to place. This is ascribed to local differ- 

 ences in the amount of evaporation, and to the 

 influx of springs which are not seen at the sur- 

 face. For some of the constituents the water 

 is nearly at saturation point. Differences of 

 temperature are also apt to cause slight differ- 

 ences in composition. 



In the determination of the acidity due to the 

 fixed and the volatile acids of wine by J. A. 

 Mliller, the determinations of potassium' bitar- 

 trate and of tartaric acid, succinic acid, and tan- 

 nin having been effected, the acidity of the fixed 

 acids enables the analyst to find the quantity of 

 the other acids, such as the malic, or of acid 

 salts that may be present. On the other hand, 

 the standard of the volatile acids shows whether 

 the wine examined is sound or diseased. 



The method of Dr. Robert Koch for the detec- 

 tion of cholera bacilli requires that, while ob- 

 serving the well-known precautions, a little of 

 the suspected water be added to a solution of 

 peptone and allowed to stand at 37 C. If there 

 are in the material any cholera bacilli capable of 

 development, they increase rapidly at the tem- 

 perature mentioned in from six to twelve hours. 

 In consequence of their avidity for oxygen, they 

 collect on the surface of the liquid, where under 

 certain circumstances they form a fine film, 

 distinctly visible. On the microscopic exami- 

 nation of a drop of the liquid from the surface 

 the characteristic comma bacilli are seen in 

 prodigious numbers. The bacilli will also de- 

 velop in their characteristic colonies in from 

 twenty-one to twenty-four hours when dropped 

 upon gelatin plates. 



A quantitative method of separating iodine 

 from chlorine and bromine, by D. S. Macnair, is 

 based on the fact that, when treated with chromic- 

 acid mixture, silver iodide is converted into the 

 iodate, while silver chloride and bromide are con- 

 verted into the sulphate. 



On account of the generally great stability of 

 organic fluorides, the determination of fluorine 

 in gaseous compounds presents some difficulties. 

 In a method recommended by Maurice Meslaus, 

 when the combustible organic fluorides are 

 burned in oxygen, the fluorine is transformed 

 into hydrofluoric acid if the molecule contains 

 the quantity of hydrogen necessary for this trans- 

 formation. We may then perform a volumetric 

 determination of this acid by means of an alka- 

 line solution, or convert it into calcium fluoride 

 and thus weigh the fluorine. 



Meeting some difficulty in removing suspended 

 finely divided particles of clay from water, Francis 

 Watt, after experimenting with various precipi- 

 tates which could be produced in the water and 

 carry down with them the troublesome particles, 

 found the formation of aluminum hydrate by add- 

 ing alum or some other suitable aluminum salt and 

 precipitation with lime water efficient. It then 

 occurred to him that the method might be ap- 

 plicable for purifying water from micro-organ- 

 isms. He, however, substituted ferric chloride 

 for the alum. This was filtered in fully saturated 

 solution through sterilized filter paper, and small 

 quantities of the water were introduced into nu- 

 trient solutions. In practically every case no de- 

 velopment of micro-organisms took place, even 

 when the solutions were kept for more than a 





