302 Manurial Properties of Claij from Gas- Works. 



fittings and the production of compounds which cannot he dis- 

 cussed here. It is enough to observe, that all ammonia anci every 

 other nitrogen compound supplied in gas was so much loss of 

 food and money. 



Having determined the source of supply, it became necessary 

 to find means for making it available. To prevent the recountal 

 of experiments which do not bear upon the great question of 

 adding to our food-producing power, it may suffice to say that 

 clay presented itself as likely to fulfil all the conditions which 

 must be satisfied in the solution of this problem. Numerous 

 investigations had made me familiar with its properties, and I 

 expected that it would abstract from gas, and retain firmly, the 

 elements of fertility which it was desired to obtain without injury 

 to the illuminating power of the gas, and at a cost which would 

 render it practicable on any scale. The purest available clays 

 were first tried, but experiment soon showed that any clay or 

 aluminous earth would accomplish the purpose thorouglily. Then 

 arose the great difficulty : were the substances thus absorbed 

 suitable for agricultural use ? Might not some one or other 

 render all else useless ? Nothing short of trials in the field could 

 answer these latter questions, and yet theory and known facts 

 afforded a strong probability that all the substances absorbed by 

 the clay were suitable plant-food. Ammonia, its carbonate and 

 sulphate, which were all absorbed by the clay, or produced as 

 the result of subsequent decompositions, were well known and 

 valuable fertilizers, and all doubt about these was at an end ; but 

 the same could not be said of sulpliocyanide of ammonium and 

 other metals which the clay took up and retained in considerable 

 quantities. But still it was difficult to believe this compound to 

 be injurious. Sulphocyanic acid is found in the saliva of man 

 and the sheep, and must either be taken in the food as such or 

 produced in the bodv by the vital processes, wliich furnish a 

 considerable number of the analogies of substances obtained 

 from the distillation of coal. Mustard-seed, again, is known to 

 contain the sulphocyanide of all_yle. Horseradish and Alliaria 

 officinalis contain the same substance. The garlic and common 

 onion contain an oil which differs but little from that of mus- 

 tard, &c. With these examples of analogous compounds in 

 the animal body and in vegetables, there seemed little risk in 

 applying sulphocyanides in quantity. 



A trial of this manure on half an acre of onions, sown July, 

 1857, strikingly shows its beneficial action upon this crop. The 

 whole plot was well-manured in the ordinary way, and about 

 four-fifths dressed with this in addition. Where this was put, 

 the crop was fully double that on the part left for comparison, 

 A wholesale dealer in such articles 2)urchased tljc crop on the 



