TRANSACTIONS OP THE SECTIONS. 4? 



dilution with water maybe applied to the vines by means of either a sponge, brush or 

 sj'ringe. A saturated solution of pentasulphide of calcium may be diluted with from 

 12 to 20 times its volume of water previous to being employed. 



On a Neto Method for determining the Commercial Value of Oxide of 

 Manganese. By Astley Paston Price, Ph.D., F.C.S. 



It is well known that several methods have been described for determining the 

 commercial value of oxide of manganese, that is to say, for estimating the amount of 

 available chlorine capable of being obtained from a given sample of manganese. 



There are, however, certain practical inconveniences attendant on the employment 

 of many of these processes, most of them demanding an amount of time and manipu- 

 lation which it is most desirable to obviate. 



The method I have for some time employed, and which I have found to give accu- 

 rate results, is based on the conversion of ai'senious into arsenic acid by means of 

 chlorine, and the transformation of arsenious into arsenic acid by the employment of 

 a solution of hypermanganate of potash. 



The specimen of manganese under examination is dissolved in a normal hydro- 

 chloric acid solution of arsenious acid ; and the arsenious acid remaining unchanged 

 into arsenic acid is determined by a standard solution of hypermanganate of potash. 

 In employing a solvent containing a reducing agent, it will be found that the solution 

 of the oxides of manganese is materially facilitated, and may be effected at a low 

 temperature in a very short space of time. 



In adopting this method, some difficulties presented themselves : — • 



On dissolving arsenious acid in hydrochloric acid, terchloride of arsenic is given 

 ofi^ and it becomes difficult to obtain a correct normal solution. This difficulty is 

 avoided by dissolving the arsenious acid in a solution of caustic potash, and then 

 adding the alkaline solution to an excess of hydrochloric acid. 



Another difficulty occurred in effecting the solution of the oxide of manganese in 

 the ai-senical solution, as in proportion to the elevation of temperature does the loss 

 of terchloride of arsenic increase. This source of error is prevented by employing a 

 dilute acid solution of arsenious acid, and adapting one of Will's nitrogen bulbs, con- 

 taining a solution of potash, to the flask in which the oxide of manganese is dissolved. 

 Any terchloride of arsenic which may pass over is there effectually retained, provided 

 solution be effected at a low temperature. The normal solution of arsenious acid is 

 made by dissolving 113'.53 grs. of arsenious acid, corresponding to 100 grs. of per- 

 oxide of manganese, in a solution of potash, and then adding hydrochloric acid until 

 the solution occupies 100 measures. 



A standard solution of hypermanganate of potash is obtained by diluting, for 

 example, .5 measures of the normal solution of arsenious acid, corresponding to 5 grs, 

 of peroxide of manganese, and then determining the number of measures of the solu- 

 tion of hypermanganate of potash that are required to transform the arsenious acid 

 therein contained into arsenic acid. 



These two solutions being obtained, an estimation of the value of a specimen of 

 oxide of manganese may be expeditiously and accurately made. 



Ten, or any number of grains of the specimen under examination, are placed in a 

 small flask, to which 10 or more measures of the normal arsenical solution are added, 

 and to the flask is adapted one of Will's nitrogen apparatus, containing a solution of 

 potash. The flask is then placed in a water-bath, or a gentle heat is applied until 

 solution is effected. The contents of the flask, after having been allowed to cool, are, 

 together with the solution of potash, transferred to a larger flask, and diluted with 

 water. The amount of arsenious acid remaining unchanged is then determined by the 

 addition of the standard solution of hypermanganate of potash, and the quantity thus 

 indicated being deducted from the number of grains of arsenious acid employed in the 

 first instance, will give the value of the specimen submitted to analysis. 



In order to obtain correct results by this method, it is of course necessary that the 

 hydrochloric acid and the potash employed should be free from sulphurous or nitric 

 acid, or any other reducing or oxidizing impurities. 



