$0 Experinicnts on riatina. 



fufficieiitly to acquire the brilliancy of the white kind tifett 

 in commerce. 



Vll. Of the EJfeils of the KitrO'inuriat'tc Acid on Flatiua. 



I cnmpofecl this acid with the nitric and muriatic acids, 

 I fliall mention hereafter the proportions bell calculated to 

 effeft this folution. 



Four hundred grains of crude platina well picked, which 

 had been traufmitted to me by Don Cafimir Ortega, being 

 treated in this acid until it had lo(l all its adion, there re- 

 mained a black matter, which, when wadied, and collefted 

 together in a china cup, was found to weigh lo^ grains, or 

 Z pounds lo ounces per cent. 



The fame quantity (400 grains) of crude white platina, 

 which I received from Don Domingo Fernandez, left fix 

 grains of a black reliduum, or one and a half per cent. 



An equal quantity of the fame kind, of which the largeft 

 particles were fclecled, left 14 grains, or 3^ per cent., of a 

 black refiduum. Thefe three experiments give a mean pro- 

 duct of about 3j per cent. 



Vlir. Of the criule Black Platina. 



Four hundred grains of the platina of Don Pedro d'Avila 

 left a refiduum of 7 grains, or I pound la ounces per cent. 



Four hundred grains of the fame left a black refiduum of 

 9 grains, or 2 pounds and a quarter per cent. 



An equal quantity of the largeft particles of the fame left 

 a refiduum of 3 per cent. Thus the mean produ6l of the black 

 kind was 2 pounds 12 ounces per cent. 



It is here fecn that there is a very remarkable variation in 

 the quantity of thefe refiduums : it arifes, firll, from the verv 

 variable action of the folvent, which more or lefs deftroys 

 the fubftance of the refiduum; and, in the fecond place, 

 from there being fomctimcs found in thefe refiduums parti- 

 cles of that metallic fand of which we have fpoken, and 

 which are generally pretty large, and imbedded, as it were, 

 in the heart of the platina. This fact has been obfcrved alfo 

 by Guyton. 



IX. Of the Graphite of Platina . 



The refiduums of which we have fpoken are nothing elfc 

 than graphite or plumbago: it burns llowly by the blow- 

 pipe, inflames nitre, and deprives the arfcnic acid of its oxy- 

 gen ; it leaves fliining or giofly traces on paper; when ex- 

 polcd to heat, it lofcs neither its foftncfj to the touch, nor its 



property 



