1822.] On a Deposit found in the Waters at Lucca. 199 



oxide of Cadmiuniy with which, however, in other chemical 

 properties, it remarkably corresponded. 



In subsequent trials 1 obtained a yellowish oxide, similar in 

 colour and in chemical characters to that which I have from 

 Prof Stromeyer. It changes to a smiff-hroicn and even black 

 colour when exposed to heat before the blowpipe, and regains 

 its own colour afterwards when cold. Five hundred grains of 

 zinc yielded exactly a single grain of this oxide hy the process 

 I have described ; so that allowing, according to Stromeyer, that 

 100 parts of the oxide of cadmium contain 14-352 of oxygen, the 

 proportion of metallic cadmium in 2-lOths of a grain of the oxide 

 (which is all I had obtained from 100 grains of zinc) would 

 equal ■^-^^ of a grain nearly, and all the cadmium which, in the 

 metallic state, is contained in 10,000 pounds weight of metallic 

 zinc is nearly equal to 17 pounds. The cadmium, therefore, in 

 this alloy exists nearly in the state of the pure gold in our last 

 silver coinage, and in very small quantity. But to proceed with 

 the other chemical quahties of the liquid I have mentioned : 



2. Phosphate of soda causes a while pulverulent precipitate, 

 which is redissolved by adding liquid ammonia, 



3. Liquid caustic potass causes a white precipitate which is 

 not soluble by adding the potass in excess. 



4. Zinc immersed in the solution becomes invested by a pre- 

 cipitate of a leaden hue, which, after solution in muriatic acid, 

 exhibits the characters o^ metallic cadmium. 



5. Sulphuretted hydrvgen causes a precipitate which is at first 

 of an orange-yellow, and afterwards of a dingy yellow colour. 



6. All these precipitates, when exposed to the action of the 

 blowpipe upon platinum or charcoal, have the habitudes of 

 Cadmium. But if any chemist shall hereafter be able to prove 

 that a substance may possess all the characters I have enume- 

 rated, and yet, after all, not be Cadminvi, no one wi]l be more 

 thankful for the inteUigence than your humble servant. 



I remain, dear Sir, &c. 



Edward Daniel Clarke. 



Article IX. 



Memoir on a Deposit found in the Waters at Lucca. By Sir 

 Humphry Davy, Bart. President of the Royal Society, Lon- 

 don, and Member of the Royal Academy of Sciences, Naples.* 



The waters of the baths at Lucca, at the spot where the tem- 

 perature is the greatest ; that is to say, in what are termed the 



* From the Memoirs of the Royal Academy of Sciences at Naples. 



