10 REPORT 1877. 



Modification II. — The above process, with the following precautious, was 

 recommended by Dr. Presenilis in a communication to this Committee : — 



" To make sure not to keep any chloride of sodium along with the chloride 

 of platinum and potassium, I first extract the chloride of platinum and 

 sodium with spirits of wine of 80°, and then wash the chloride of platinum 

 and potassium with a few cub. ccntims. of water, drop by drop ; then I 

 evaporate this solution, adding a little chloride of platinum, treat the small 

 precipitate again with spirit of wine, and add the small quantity of chloride 

 of platinum and potassium to the bulk." 



Modification III. — The third modification is that of Drs. Frank and 

 Berrand, of Leopoldshall. These chemists employ only about *2 grm. of the 

 potash salt, and manipulate like Freseuius, but they wash the precipitate 

 with alcohol of 98 per cent., which is practically absolute. They dry tho 

 precipitate at 110° C. 



Modification IV. — The fourth modification is that of Mr. It. E. Tatlock, 

 who thus describes it in his communication to the Committee :— " A portion 

 of the solution, equal to 10 grains of the original sample, is delivered into a 

 small basin, diluted with 400 grains or so of water, and acidified slightly 

 with hydrochloric acid. About 500 grains of platinic chloride solution (con- 

 taining at least 25 grains of platinum) are added, and the fluid evaporated 

 nearly to dryness on a water bath. A few drops of water are then added to the 

 residue, and the evaporation repeated to expel the excess of hydrochloric 

 acid. About 50 grains more of tho strong platinic solution arc mixed with 

 the precipitate, and the whole stirred well and set aside in a cold place for 

 at least an hour, with occasional stirring. The precipitate is then thrown on 

 a very small filter (unweighed), the basin rinsed out with about 10 drops 

 more of the platinum solution, and the precipitate on the filter washed with 

 10 or 15 drops more. The basin and the filter and contents arc then washed 

 with the smallest possiblo quantity of alcohol of 95 per cent, strength, and 

 dried at 100° C. The dried precipitate is transferred as completely as 

 possible to a small capsule, in which it is further dried until it assumes a 

 distinct, orange colour, and weighed. The filter, with a trace of adhering 

 precipitate, is ignited on a crucible lid, and the residual metal, with its cor- 

 responding chloride of potassium, calculated to potassio-platinic chloride, and 

 the weight added to that of the precipitate." 



From the above descriptions it will be seen that tho chief points of 

 difference in the processes arc as follows : — 



Freseuius (Process I.) uses moderately strong alcohol (80 per cent.) for 

 washing the precipitate ; but in his modified process he subsequently uses a few 

 centimetres of water, and recovers any potassium salt thus dissolved. 



Frank and Berrand use a very small weight of the sample and wash with 

 absolute alcohol. Tatlock washes first with a strong solution of platinic chloride, 

 and then with strong alcohol. In all editions of his ' Quantitative Analysis ' 

 prior to the 7th English, Freseuius directs the drying of the precipitated 

 chloroplatiuate at 100° C. In the last edition drying at 130° C. is recom- 

 mended. Frank and Berrand use 110° C. Until after the conclusion of the 

 investigations the words "further dried" in Tatlock's method were understood 

 by the Committee to signify longer drying at 100? C, but it has since been 

 learnt that drying at a somewhat higher temperature was intended. 



In all cases in which the temperature used for drying the precipitate is 

 not expressly stated, the Committee employed 100° C. The experiments 

 instituted to ascertain the influence the temperature used in drying had on 

 the weight of the precipitate showed a loss of -067 per cent., by subjecting 



