346 On. the Uses of the Dorsal Vessel. [Nov. 



iron pot, from which it is ladled out, and cast into pigs of a deter- 

 minate weight. 



A considerable quantity of metallic lead remains entangled in the 

 slag. To obtain tin's the slag is put into a blast furnace, and urged 

 by a heat sufficient to bring it into perfect fusion. The lead now 

 falls down through the liquid, and is collected at the bottom of the 

 furnace. The liquid slag is run into a reservoir of water, where it 

 breaks into a black powder, having all the appearance of black 

 glass. I analysed a quantity of this black glass, and found it a 

 compound of silica, lime, and oxide of iron, with some alumina, 

 oxide of lead, and oxide of antimony. I think it unnecessary to 

 state the proportions, because they must vary according to circum- 

 stances. The earthy matters were no doubt partly mixed with the 

 ore, and partly contained in the pit-coal employed to reduce the 

 galena. The pit-coal is probably the matter that furnishes the iron, 

 though some pyrites may be occasionally present in the ore. I 

 forgot to mention it as a substance occasionally met with in the 

 veins. 



I found the specific gravity of this black slag 3"225. When 

 mixed with lime it forms an excellent water mortar, and is sold for 

 that purpose to a considerable amount. As the mortar dries it 

 becomes yellow. I should conceive this to be owing to some oxide 

 of lead which the slag contains, and which the lime gradually 

 separates. 



This black slag is again searched for lead, and the quantity ex- 

 tracted from it more than repays the expense of the process. 



The lead, when the proportion of silver which it contains will 

 cover the expense, is converted into litharge by exposure to heat 

 upon a test. The litharge is blown off, and the silver remains 

 behind. The litharge is again melted in a furnace with common 

 pit-coal, which speedily reduces it to the state of lead. When thus 

 treated it is known in commerce by the name of refined lead, and 

 is the purest and most valuable sort of that metal. 



{ To be continued.) 



Article V. 



Observations on the Uses of the Dorsal Vessel, or on the Influence 

 which the Heart exercises in the Organization of articulated 

 Animals, and on the Changes which that Organization expe- 

 riences when the Heart or the Organ of Circulation ceases to 

 exist. By M. Marcel de Serres.* 



Of all the questions which remain to be solved in the anatomy of 

 animals without vertebrae, there are certainly few more interesting 



* Translated from the Magasin Enejclopedique, iii, 10. May, 1814. 



