1806.] 



Proceedings of Learned Societies. 



25i 



3. A hundred pnrts of the fame mafs 

 were treated with dilute nitric acid, 

 which dillblved the greatcft piirt of it, 

 while that which remained difplayed a 

 white colour and a cryftalliue form. 

 This fubftance, wlien feparated from the 

 litjuor, melted upon biuning coals, af- 

 fumed a black colour, and was diliipated 

 in fumes without leaving any lead in a 

 metallic ftate : circumltances which 

 clearly indicate that this fubftance was 

 common muriate of lead. The portion 

 dilVolved in the nitric acid, when evapo- 

 rated by a !j;eat!e heat, furniflied cryltals 

 of nitrate of lead, among which there a^i- 

 peared a few ncedle-lhapcd cryllals of 

 muriate of lead, v.liich had been diffol- 

 ved by the nitric arid. 



4. A liundred other parts of the mafs, 

 when treated with boiling-water, did not 

 appear to underp;o any change, and the 

 liquor fcarcely exhibited any lic:ns of the 

 p)cfence of lead with the hydrofulphurct 

 of potafli. » 



From thefe experiments it appears dc- 

 monfirated, — 1. Ihat the litharge em- 

 ployed for the dcco:npofition of nmriate 

 of foda, is a muriate of lead with an ex- 

 cels of oxide. — 2. That the cauftic alka- 

 lies do not decompofe this fait, but 

 merely dillolve it. — 3. That it is in con- 

 fequence of the atlinity of the muriate of 

 ^eiid for this oxide, that the lithan^c de- 

 coinpofes i'ea-falt. — i. That it is tiiis fu- 

 perabundant quuiitity of oxide in pro- 

 portion to the common muriate of lead, 

 v.hich imparts to this fait the property of 

 aifumins a citron-colour, by means of 

 heat, which never happens to the conv 

 iiion muriate of lead. — 5. That it is the 

 oxide which renders this muriate of leiid 

 nearly infoluljle in water. — 6. Tb.at it is 

 the oxide which tlie nitric acid holds in 

 foiution with which it forms nitrate of 

 lead, whilft it leaves only neutralized mu- 

 riaieoflead. 



So true is it that the oxide of lead ne- 

 ver efi'ecls the decompofition of muriate 

 of foda but in formin;^; a muriate of lead 

 with an excefs of oxide, that, when we 

 decompofe the connnon muriate of lead 

 by cauftic foda, we never can entirely 

 free it from all its muriatic acid. There 

 sdways rcmnius a fuiiicient (juantity to 

 prefcrvc the lead in that Hate in wliich 

 It i.s found after the dcciiifipoiition of the 

 muriate of foda ; which is dcmonftrated 

 by the citron-colour which it aifumci on 

 the application of heat, by its decompo- 

 fition will) the nitric acid, by the fepara- 

 yoik of the coiiunua uiuriatc of lead, and 



the formation of the nitrate of lead which 

 takes place during this operation. 



It is therefore evidently in confe- 

 quence of a double affinity that the ox- 

 ide of lead decompofes the muriate of 

 foda, by the attraction of the oxide of 

 lead for the nmrii^tic acid, and of the 

 muriate of lead for an excefs of oxide. 



Hence we may readily explain why fo 

 much oxide of lead is requilite to elicit 

 the complete decompofition of the mu- 

 riate of foda, hnce that tive-fixths at Icalb 

 of this oxide are employed, not to de- 

 compofe the fea-falt, but to form the mu- 

 riate of lead with an excefs of oxide, and 

 that the fourth at moll of this oxide 

 combines with the muriatic acid, in the 

 ftatc of a true muriate of lead. 



Hence it may be atllrmcd, that the li- 

 tharge completely decompofes the mu- 

 riate of foda, when in a lutlicient quan- 

 tity, and that the foda never wholly de- 

 compofes the muriate of lead, in what- 

 ever quantity it may be employed. 



If the carbonate of lead cannot de- 

 compofe the muriate of foda, it follows 

 that the carbonate of foda mull pcrfettly 

 decompofe the muriate of lead ; and this 

 is in fai-t confirmed by experience. 



liefides, the muriate of lead is not the 

 only fait of this kind which polfcffes the 

 property ofabforbiua; an excefs of oxide. 

 Tlie fulphatc, and the nitrate, and per- 

 haps many others, poiiefs it alio. A 

 proof of the truth of this is furniihcd by 

 the decompoiition of the nitrate and ful- 

 phate of lead, by cauftic alkalies, and 

 particularly by ammonia. There always 

 remains in the oxide of lead a fmall 

 quantity cf theft- acids, the (irlt of which 

 is detected by the nitrous vapours which 

 are difengaged on heating the wallied 

 precipitate ; the fecond by a refiduum 

 left by the nitric acid, with wliich the 

 precipitate obtaided from the ful])hate of 

 lead was treated, and which reiiduum is 

 itfelf nothing more thanafuljjhateof lead. 



Vauquelin concludes his obfervations 

 by fuggcitingihc probability that the de- 

 compoiition of muriate of i'lda by lime is 

 eifected in a liiViilar manner ; aiid he in- 

 forms the Inftitute that he is about to 

 enter upon a courfc of experiments in 

 order to afcertdn the truth of this con-i 

 jefture, which fliali in due time be laid 

 before the Society. 



.ROYAL SOCIETV OF LOXDON. 



Dji. HER^CHF.r, has laid before this 

 learned body, a paper " On the Quan- 

 tity and Velocity of the Solar Motion," 

 which 



