ACTION OF PLATINA A\*b MERCtJKY-. lH 



•^which does not happen when it is alone, I have tried to pro- 

 duce the fame efted with other metals and platina, but I have 

 not obfeived any thing iimiJar. It is therefore fair to conclude, 

 that when a folution of platina is precipitated in a metallic ftale 

 by a folution of green fulphate of iron, either filver or mercury 

 IS prefent. 



The precipitation of a mixed folution of platina and filver Nitrate of filvcf 

 requires no further caution than to free the fait of platina as ^'j^^.'^ to mur. 



» ... . platina throws 



much as poflib'e from muriatic acid ; for as I obferved in my down a triple 



former Paper, the elfe6t of nitrate of filver poured into muriate, '"""/'f.'^*^ °^ P'* 



r , . . t . . ,- ■ /.*"^ filver. 



ot platina, is to produce a precipitate, not ot muriate or 



(ilvefi but of a triple muriate of platina and filver. It was 

 hy this experiment that I then proved the affinity of thefe two 

 metals; for when filver is not prefent, muriate of platina is 

 among the moft foluble falls. The befl: method of prefent ing Predfe merh<vt' 

 the three folutions of platina, filver, and green fulphate of iron ^^ pre^ip. pi, and 

 to each other, \% firft to pour the filtered folution of the laft tailic ftate by 

 info the folution of platina, and then, after mixing them tho- ^"^P^* *»■««• 

 roughly together, to add the folution of filver by degrees, and 

 to ftir them conftaiUly. In this, as in all fimilar opefations, « 

 (he prefence of all acids, falts, &c. excepting thofe ne- 

 celTary for the operation, (liould be avoided ; and if proper 

 proportions have been ufed, and ail circumftances attend- 

 ed to, the precipitation of thefe two metals will be very 

 complete. 



But the precipitation by a folution of mercury requires to be The fame, but 

 further contldered, as the ftate of oxidizement of this metal. ^•^'- ^'"'"t'^'^of 



IT t • » ■ . • 1 • • »• T. I 1 • mercury. 



as well as the acid in which it is dilfolved, produces a confi- 

 derable modification in the refult. In the firfl place the oxide, 

 at the minimum of oxidizement, difTolved in muriatic acid, is 

 unfit for the experiment ; and even the red oxide difTolved in 

 the fame acid, or corrofive fublimate, is not the moft advan- 

 tageous. When a warm folution of the latter is poured info a 

 mixed folution of platina and green fulphate of iron alfo 

 warm, as in the cafe of filver, thefe fubltances are brought 

 into cental under the moft favourable circumftances. Yet 

 even thus the precipitation is flowly and imperfe6lly formed, 

 often not till feveral hours have elapfed ; and fometimes a 

 very great deficiency of weight is obferved, between the quan. 

 titles ufed and Ih^fe recovered dire^lly by this method. If a 

 folution of nitrate of mercury be ufed, the efR-c^ is produced 



more 



