i 



Experiments on Platina. i2^ 



5th, As the muriatic acid conftitutes the ftrongeft part of - 

 the folvent of crude platina, in the commencement of the 

 labour care muft be taken that the heat docs not attain to the 

 point of ebullition; becaufe, ift, At that temperature the 

 muriatic acid eafily acquires aeriform expanfion; 2d, The 

 tendency which it has to feparate itfelf from the mixture is 

 ftill Wronger when it begins to be oxygenated. From what 

 I have obferved, the folution ousrht never to begin at a heat 

 fuperior to 60 or 70 degrees of Reaunuir (135"' to J57" Fahr.), 

 and it is then effected, without lofs of acid, with all the ra- 

 pidity poffible. In a word, the liquor ought not to be boiled 

 till the eflcrvefcence decreafes. 



The five confcquences which we have here deduced, and 

 which are nothing but the refult of the fame experiments, 

 give us the true principles of the art of diflolving platina. 



If we now compare the proportion of platina with the 

 nitro-muriatlc acid, we fhall find that the quantity diflblved 

 rifes fomewhat above the eighth part of the weight of the 

 folvent. This proportion, hcvwever, is fubjeft to fome varia- 

 tion ; for the fame acid empioyed in fimjlar circumftances 

 diflolves fometimes a lefs quantity, though in general it de- 

 viates very little from this proportion. 



XV. On the Utility ivhich may be derived from the Trodu£is 

 of this Diftillation. 



In operations on a large fcale, oeconomy being one of the 

 moll important objc6ts, it may be readily conceived that the 

 ac id produ^U in queltion ou2:ht to be carefully collecled, and 

 that the concentration fliould be carried as far as poffible to 

 increafe thcl'e products; for the expenfe of thefe folutions will 

 be fo much more moderate, if the fame quantity of acids can 

 be employed for a greater quantity of platina. That I mitiht 

 be better enabled to afcertain the advantages in this refpe6l, 

 I made tlie following experiment: 



I dillill'.d, to the confidence of concrete honey, a folution 

 fimilar to that of the third experiment, the produft of which 

 I carefully collcfted ; and by thefe means I was enabled to 

 obferve in this operation three different periods. 



In the firjl the diftillation, which began at a heat of nearlv 

 70 degrees (or about 150- Fahr.), was accompanied with 

 cflerveicence and a difengagement of nitrous gas, which, as 

 Lavoifier obfervcs, dcferves to be examined, and elpecially 

 the moment when the oxide of azote or azotic oxide manifefls 

 ilfclf. 



In iho. fecond period , the cfTervefcence was followed by ebiil- 

 ^itionj and here no nilro..-.s gas wasdiflinguiflied; aweakco- 



lourlcfs 



