TBANSACTIONS OF SECTION B. 559 



As the above crops were not the same, and the quantities of manure emploj^ed 

 differed and were applied at difl'erent times, no exact results maybe deducible from 

 the above trials ; but as the experiments were all witli cereals, we are able to draw 

 general conclusions from them, which are not unimportant, as to the effects of 

 magnesia as a manure, and 



First. — As sulpliate of soda, when used alone, proved in each case prejudicial, 

 we may assume that at least it did not materially assist the result when mixed ■w'ith 

 rape dust or sulphate of magnesia. 



Secondly. — As rape dust, when used aloue, gave orAj a certain increase to the 

 crop, any further increase when used with sulphate of magnesia must be due to 

 tlie influence of the latter substance, and 



Thirclhj. — As rape dust used aloue with oats decreased the crop of grain 16-6 per 

 cent., and with spring wheat only increased the crop of grain by 7 per cent., whereas 

 when used in conjunction with 84 lbs. only per acre of sulphate of magnesia 

 ( = 13'6 lbs. of magnesia), as a top dressing with winter wheat the increase rose to 

 nearly 16 per cent., it is reasonable to suppose that some portion — indeed a con- 

 siderable portion — was due to the influence of the sidphate of magnesia, small as it 

 was, and not to the rape dust as a single agent. So far as the rape dust improved 

 the result it may be supposed to be attributable to the influence of the magnesia, 

 to which substance Liebig, as we have seen, assigns a very definite part in the 

 formation of the seed. 



It must be borne in mmd in considering the question, how far a soil is likely to 

 be improved by an increase of the amoimt of magnesia in it, that crops remove 

 from the soil the greater portion of then- mineral constituents within a short space 

 of time as compared with the whole duration of the existence of the plants, and 

 that, therefore, it must be of the greatest moment that they should be able to 

 gather them from the soil within this period. A.fter a certain time a cultivated 

 plant advances little in size and weight, although great changes occur in the dis- 

 tribution of its constituents. 



Liebig says, with manifest truth: 'As a soil may contain far more potash, or 

 map-nesia, or lime than the crop may require, yet, being diffused through a large 

 quantity of earth, the roots may be unable to collect the ingredients fast enough to 

 supply the growing wants of the plant — to such a soil it will be necessary to add 

 a further portion of what the crop requires.' 



The last experiments to which I shall refer are those of Dr. Pincus, of Insterburg, 

 which Liebig characterises as most important, both on account of the careful manner 

 in which they were conducted and the conclusions drawn from them. Three plots 

 of ground were selected lying close together, each of about five-eighths of an acre ia 

 extent, from the middle of a large clover field. The clover crop had a very promising 

 appearance and the plants were then about one inch high ; one of the plots was 

 manured with 1 cwt. of gypsum, the second with the same quantity of sulphate of 

 magnesia, and the intervening plot was left immanured. When all were in flower 

 the clover was mown, and the following were the results : — ■ 



Per f acre. 



Without manure , 2r6 



With gypsum (sulphate of lime) .... 30-6 

 With sulphate of magnesia ..'... 32"4 



Or the gain with the use of the magnesic salt as a manure was just 50 per cent. 

 It is to be observed that the stems were developed by both the sulphates much 

 more than the leaves and flowers. The experiment also showed that there was no 

 proportion between the quantities of sulphuric acid found in the crops and in those 

 supplied by the two sulphates. The quantity of sulphuric acid in the two sulphates 

 was 31-12 lbs. in the sulphate of magnesia, and 44-18 in the sulphate of lime, which 

 is about 6 : 8-8. The quantities of sulphuric acid in the two crops obtained severally 

 by sulphate of lime and sulphate of magnesia were as 6 : 8 ; and on the plot manured 

 with sulphate of magnesia, which had received less sulphuric acid than the gypsum 

 plot, the amount of vegetable matter was 8 per cent, higher than on the latter. 



Liebig, from experiments made on arable soils, came to the conclusion that 

 dressing a field with sulphate of lime makes the magnesia in the soil soluble and 



