132 On the Solubility of [Aug. 



entirely to their silken habitations. Thev then not only secure the 

 general web to exclude impertinent intruders, but each individual 

 spins a thin case for itself. Here they rest in a state of torpid secu- 

 rity, till the genial warmth of spring animates them afresh, and 

 informs them thut the all-bountiful author of nature hath provided 

 food convenient for them. Thus apprized, they issue forth in the 

 day time, and in fine weather, as before ; but having acquired 

 stronger powers, and the foliage they have now to encounter being 

 more tender, they become less scrupulous in their feeding, and 

 devour the whole of it. A disposition to associate continues with 

 them till they have changed their last skins, when they usually 

 separate, each endeavouring to provide in the best manner for itself. 

 At this period they are most exposed to various enemies, and most 

 frequently attacked by the ichneumon fly. We sometimes find a 

 few continuing together to the last, when each spins a separate web, 

 in which it changes to a chrysalis. This usually takes place about 

 the beginning of June. Here, in a state of perfect quietude, it 

 remains for three weeks, when it changes to the moth already 

 described." 



Article X. 



On the Solubility of White Oxide of Arsenic in Water. 

 By M. Klaproth* 



The solubility of white oxide of arsenic in water is a property 

 which essentially characterizes it. Though the fact has been long 

 known, yet the degree of solubility has not been accurately deter- 

 mined. According to Bergman, 80 parts of water at the tempera- 

 ture of 60° dissolve one part of white oxide of arsenic, while the 

 same quantity of oxide is dissolved by 15 parts of boiling water ; 

 according to Navier, 80 parts of boiling water are requisite to dis- 

 solve one of the oxide ; and according to Hagen, 30 grains of white 

 oxide of arsenic require four ounces of boiling water to dissolve 

 them. 



These different statements induced me to endeavour to ascertain 

 the proportion ; and the result of my experiments is, that three 

 parts of white oxide of arsenic may be kept in solution by 100 parts 

 of water at a medium temperature. On that account, the statement 

 of Aschof,f that one part of white arsenic requires 200 parts of 

 boiling water to dissolve it, appeared to me extraordinary. 



As this result may occasion mistakes in medical jurisprudence, I 

 consider it as proper to point out the error of M. Aschof, and to 

 show that the new experiments which I have repeated on this sub- 

 ject have confirmed my former opinion. 



* Translated from Schweigger's Journnl der Cliimii*, vi. 2S2. 

 t Sell weigger's Journal, \.2i7. 



