CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 607 



Uniting the four analyses into one, we have — 



Total chloride of potassium used, .... =26076 grms. = A. 



„ platinum obtained, =3*4240 „ =p. 



Hence A: p = 0-76157 



and (p : A) xK 2 Cl 2 = 195-89. 



V. Set of Experiments, 



Salt analysed consisted of 33-3 per cent, of chloride of potassium, 33*3 of 

 chloride of sodium, and 33 3 of sulphate of magnesium. 

 Method exactly as in IV. Set 



Results. 



Experiment 1. 2. 3. i. 



I. Chloride of potassium taken, -26603 -26606 -26490 -26490 grm. 

 II. Platinum obtained, . . -3501 -3500 -3484 -3491 „ 



lll ' KC \7rnTxu. s,i ' e : :} ,26649 - 26641 - 26519 - 26572 - 



Error, III. - 1., . . +046 +035 +0-29 +0-82 mg. 



A = Total chloride of potassium used, = T0619 grms. 

 p = „ platinum obtained, =T3976 „ 



Hence A :p = 075980 



and(p: A) xK 2 Cl 2 = 196-34. 



Tatlock's Method. 



This method was invented expressly for the assaying of commercial potash- 

 salts, i.e., of salt mixtures similar in constitution to those which we employed 

 for our test-analyses by Finkener's method. Mr Tatlock's method, according 

 to his own description,* is as follows : — Assuming the substance to be 

 analysed to have been converted into a standard solution, a quantity equal to 

 (" 10 grains" = ) 0*6 to 07 grm. of dry salt is measured off, to be analysed as 

 follows : — For every one gramme of salt the solution is diluted to about 40 c.c. ; 

 it is then acidified with a few drops of hydrochloric acid, and mixed with 50 c.c. 

 of a " 5 per cent." chloride of platinum solution, meaning a solution contain- 

 5 centgrms. of metal per c.c. The mixture is evaporated to near dryness over 

 a water-bath, and the residue re-evaporated with addition of a little water, 

 to more fully eliminate the free hydrochloric acid. [Observe that this large 

 proportion of platinum is prescribed for all kinds of salts, rich or poor. Now 

 1 grm. each of the anhydrous salts, NaCl, MgCl 2 , MgS0 4 , demands only 1-69, 

 2*08, 1*65 grms. of platinum, assuming Pt to be equal to 198; hence Mr 

 Tatlock's intention apparently is to have sufficient chloroplatinic acid present 

 for converting all the metals into chloroplatinates, and, in addition thereto, some 



* As communicated by him to a Committee of the British Association, and published by them in a 

 Report presented to the Meeting at Glasgow, in 1876. 



