On Animnlcules, — partmdarly on the Polypes. 283 



Arsenic acts upon barytes, but not so much as potash. By 

 passing the vapours of arsenic over red barytes, a combination 

 took place, the barytes being entirely penetrated with the ar- 

 senic. On adding cold nater, no disengagement of" gas took 

 place ; but by heat T obtained a little arsenicated hydrogen gas. 



I made afterwards a mixture of su!)carbonate of soda in solu- 

 tmn and arsenic; I put it into a glass vessel to which I had 

 adapted a tube to collect tlie gas, and exposed it to a red heat. 

 The arsenic began scon to volatilize, and disengaged but a small 

 quantity of carbonic acid, which might be owing to a little of the 

 oxide of arsenic which always accompanies arsenic exposed du- 

 ring some time to the air. , The subcarbonate did not appear to 

 have experienced any alteration. 



From these observations it will be seen that arsenic has great 

 affinities to sulphur, and cspeciallv jjhosphorus; like them it 

 combines with several oxides, and like j)hosphorus it forms with 

 hydrogen gas a combination which does not possess acid pro- 

 perties. But it ought to be placed after phosphorus, because its 

 affinities are weaker, and it does not disengage the carbonic acid 

 of carbonates. 



In making these experiments I have had occasion to remark, 

 that hydrcsulphate of potash (hssolves an enormous quantity of 

 sulphuret of arsenic. I was led from that, to endeavour to neu- 

 tralize the liydrosulphate from the sulphuret of arsenic by the 

 aid of a current of hydrosu'phuric gas,' but did not succeed. At 

 the end of some days the hydrosulphate had allowed much of 

 the sulphuret to precipitate, although in a close vessel; but for a 

 long time it still preserved a considerable quantity. Hydro- 

 sulphuric gas has not, however, the propertj', like potash, of dis- 

 solving any scnsil)le quantity of sulphuret of arsenic. I would 

 compare the hydrosulphate of potash and of arsenic to the 

 pnissiate of potash and of zinc, which I have been equallv imable 

 to obtain in a neutral state. In general hydrosulphuric acid has 

 a great affinity to hydrocyanic acid ; but its tendency to form 

 triple combinations is not nearly so well marked. 



G. L. 



LXXI. On Animalcules, — particularly on the Polypes. 

 To Mr. TUloch. 



Sm, — OnoULD you think the following remarks upon an in- 

 teresting branch of natural history worthy a place in your valu 

 able Magazuie, an early insertion of them will much oblige, sir, 



Your very obedient servant, 

 Liverpool, April 12, 1017. .lOHN liyWATEK. 



That 



