112 On the presence of Arsenic in some Artificial Manures. 



from arsenic ; and to avoid all possibility of error, comparative 

 experiments with the reagents alone were made in almost every 

 step of the different investigations. 



The turnips I experimented on were grown by Mr. John Rath- 

 bone, Dimsinea, Co. Dublin; and 1 was informed that six hun- 

 dredweight of superphosphate had been used to the Irish aci'e, — 

 the superphosphate being previously mixed with peat and clay, 

 in the proportion of one part of superphosphate to three parts of 

 the mixture of peat and clay. 



These experiments appear to me to be perfectly conclusive as 

 to the power possessed, by some plants at least, of taking up 

 arsenic when it is introduced into the soil by artificial manures 

 which contain it, even when they are employed in the usual way 

 and proportions by agriculturists, and how objectionable it is to 

 use any materials in the preparation of those manures which will 

 introduce so destructive and dangerous a substance as arsenic 

 into the soil. 



I thought it would be desirable to ascertain the proportion of 

 arsenic present in the brown sulphuric acid used by one of our 

 Dublin manufacturers for the purpose of making superphosphate 

 and other manures. In 13 fluid ounces of the acid, by the usual 

 methods of determining the quantity of arsenic in such cases, I 

 obtained an amount of metallic arsenic equivalent to about 12 

 grains of arsenious acid, or 1 grain to each fluid ounce ; and the 

 ounce of acid weighing about 800 grains, the arsenious acid 

 would be ^^yth part of the weight of the acid, which would be 

 equivalent to about 2*8 lbs., or nearly 3 lbs. weight in the ton 

 of sulphuric acid. But it is probable that the generality of 

 brown sulphuric acid employed contains much more arsenic 

 than this sample I examined, its specific gravity being only about 

 i'780, whereas the usual strength of the acid is 1"845. Dr. 

 Owen Rees found 13"5 grains of arsenious acid in 12 fluid ounces 

 of commercial sulphuric acid ; and Mr. Watson, in the London 

 Medical Gazette, states that the smallest quantity of arsenious 

 acid which he detected in the same amount of commercial acid 

 was 21"3 grains. There is therefore every reason to suppose 

 that the acid usually employed for agricultural purposes contains 

 a far greater quantity of arsenic than the sample I examined ; 

 and as the proportion of sulphuric acid used in making these 

 artificial manures is very large (thus, for example, in the manu- 

 facture of superphosphates, the most valuable manure of this 

 class, about one ton of acid is used for every two tons of bones 

 employed), the quantity of arsenic present in such manures must 

 be considerable. 



These facts appear to me to have some important bearings ; 

 for though the quantity of arsenic which occurs in such manures 



