Determination of Antimony. 345 



of litmus paper is placed in the liquid, and dilute sulphuric acid 

 added until the mixture is feebly acid. Solution of starch is 

 added, and the determination, by means of iodine, proceeded with 

 in the usual manner. 



If a is the quantity of sulphuretted hydrogen corresponding 

 to 1 cubic centim. of solution of iodine, t the number of cubic 

 centimetres of the solution of iodine used, the value for the an- 

 timony is obtained from the equation 



_ Sb 4 



To test the method, 0*326 grm. of pure antimony-glance was 

 decomposed by hydrochloric acid, and the determination made 

 in the above manner. 



a=0'000803, *= 123-5. 

 Calculated. Found. 



71*48 per cent, antimony 71*74 per cent. 



28*52 „ sulphur 

 10000 



A higher degree of accuracy than this is obtained by collect- 

 ing the sulphuretted hydrogen gas in a solution of arsenite of 

 soda, and determining the rest of the arsenious acid by solution 

 of iodine. 



Mohr was the first to propose the combination of an alkaline 

 solution of arsenious acid with iodine, and he prefers this in 

 many respects to Bunsen's method. I cannot unconditionally 

 agree with him. If any alteration is to be made in Bunsen's 

 original method, the only reasons for which would be the great 

 dilution required, and the changeability of the sulphurous acid, 

 hyposulphite of soda ought to be preferred to arsenite of soda. 

 The reasons urged by Mohr against its use are not perfectly 

 tenable. That its decomposition by chlorine is different to its 

 decomposition by iodine is unimportant, as it never comes in 

 contact with free chlorine, but always with free iodine ; the con- 

 sumption of iodide of potassium which it occasions is the less to 

 be regarded, as comparatively small quantities of substance are 

 used in iodometric determinations ; that its acid solution changes 

 is equally unimportant, as it is only in contact with acid during 

 the short time of the determination. On the other hand, the 

 poisonous properties of arsenious acid are a formidable objection 

 to its use for volumetric purposes, so long as suitable substitutes 

 can be obtained. 



For the determination of sulphuretted hydrogen, arsenious 

 acid is well adapted. It affords a precision which is scarcely 

 attainable with any other means. 



Phil Mag. S. 4. Vol. 20. No. 134. Nov. 1860. 2 A 



