Prof. Bunsen o« Cacodyl Compounds co7itaining Platinum. 401 



with difficulty. It contains no more water which can be driven 

 off by any elevation of temperature. r0390 gramme of this 

 salt, dried at 140" C, burnt with chromate of lead, gave 



0-2395 water, and 0*340 carbonic acid. 



0-5491 gave 0'1290 water, and 0-175 carbonic acid. 



1-0474 gramme dissolved and precipitated by nitrate of ba- 

 rytes, gave 0-04746 sulphate of barytes. 



These determinations give the following composition : — 



( 



Carbon C4 . . 305' 7 



Hydrogen H^ . . 87-4 



Arsenic Asj . . 940*0 



Platinum Pt . . 1233-3 



Oxygen O3 . . 300-0 



Sulphuric acid S O3 . 501-2 



The characters of the chloride of cacoplatyl are so well 

 marked, and its relations to other bodies so manifest, that we 

 cannot be in doubt for a moment as to its rational composition. 

 One glance at its empirical formula will satisfy us that here, 

 as in the compounds of cacodyl, the most electro-negative 

 element, chlorine, can by analogy be replaced by bromine 

 and iodine, just as oxygen is replaced by sulphur. The man- 

 ner in which this substitution takes place is not different from 

 that which we observe in the inorganic saline compoimds. 

 The chloride of cacoplatyl, treated with the iodide of potas- 

 sium, gives np its chlorine to the potassium, while the iodine 

 goes over to the other element of the formula, from which the 

 potassium has withdrawn the chlorine. The order of affinity 

 of chlorine, iodine, and bromine, for the substance in question, 

 bears a perfect analogy to what we observe in the inorganic 

 haloid salts. The iodine is here set free by chlorine and bro- 

 mine, as in these salts, while bromine is removed by chlorine 

 only. 



Such an agreement in relation shows a similarity in the 

 form of the groups of the elements, and indicates that here, as 

 in the inorganic haloid compounds, there are two divisions in 

 the formula, one of which represents the metal, the other the 

 lialogenous body or salt-radical. We can express it thus: — 

 Pt02C,H7As2 + CI. 



The first division of this formula, which I have called caco- 

 platyl, represents a peculiar and remarkable radical, forming 

 classes of compounds possessing great interest, and giving an 

 insight into the relation in which the vegeto-alkalies stand with 

 regard to organic radicals. As the vegeto-alkalies, when 

 heated, give off ammonia, so our compound gives off water, 



Phil. Mag. S. 3. Vol. 20. No. 132. May 1842. 2 E 



