IS 11.] Wh'ite Oxide of Arsenic in Water. 133 



A. — To determine the solubility of the oxide in cold water, I 

 introduced 20 grains of it, previously reduced to a fine powder, 

 into a flask containing 10 ounces of water of the temperature of 

 GO . Tli is mixture was left for 24 hours, being often agitated in 

 the mean time. The undissolved portion, collected upon a filter, 

 and well dried, was eight grains. Of consequence, 12 grains had 

 been dissolved. The result of this experiment is, that 1000 parts 

 of cold water dissolve only 2-i- parts of white oxide of arsenic. 



B. — Water can only saturate itself with this oxide at the boiling 

 temperature. To ascertain the degree of solubility, I boiled for a 

 quarter of an hour 200 grains of white oxide of arsenic in powder 

 in four ounces of water in a phial. As soon as the undissolved part 

 was deposited, I decanted off the liquid portion, which weighed 

 1800 grains. This liquid, evaporated in a capsule, the weight of 

 which had been determined beforehand, left for residue 140 grains 

 of white oxide of arsenic. Therefore 1000 parts of boiling water 

 take up 77-3- of white arsenic. 



C. — It was particularly important to know how much white oxide 

 of arsenic the boiling water would retain after it was cold. For 

 this purpose 10 ounces of boiling water were saturated with white 

 oxide of arsenic in powder. After cooling, I left the phial for three 

 days in cold water, during which time some white arsenic separated 

 in the crystalline form. Five ounces of the decanted solution were 

 evaporated in a capsule previously weighed. The residue, when 

 well dried, weighed 72 grains, and was white oxide of arsenic. 

 Hence it follows that 1000 parts of water retain in solution, after 

 cooling, 30 parts of white oxide of arsenic, or 100 parts of water 

 retain three parts of the oxide. It is obvious that the cold of winter 

 may produce some modification in these proportions. 



D. The crystalline form of the white oxide of arsenic obtained 

 by evaporation may lead to the suspicion of the presence of water, 

 or that the oxide is in the state of an hydrate, which might account 

 for the augmentation of its weight. To determine this point, I 

 boiled three ounces of water in a phial with 100 grains of arsenic. 

 Alter a quarter of an hour's boiling, all the arsenic was dissolved. 

 The clear solution, being evaporated to dryness, left 100 grains of 

 v. iiite oxide of arsenic in a crystalline form. This experiment 

 shows that oxide of arsenic does not combine with water when dis- 

 solved in that liquid, and evaporated to dryness. 



Article XI. 



On u Bnl of fossil Sheik on the Hunks of the Forth. 

 liy John Fleming, D.I). F.R.S.E. 



Tab Led of ihells which 1 am about to describe occurs to the 

 ward of the town of Borrow ttOUnneiS in the county of Linlith- 

 G 



