president's address — SECTION B. 77 



solidification are always from a liquid coulainiiig a relatively large 

 amount of impurity. There will probably be weakness in having the 

 first particles of solid welded together by a solid of different composition. 

 Apart from this, the manner in which the solid particles are deposited 

 from a mother liquor varies, we know, greatly with the composition of 

 the liquid. The appearance of many crystalline solids sold commercially 

 is made to suit the eye of the purchaser by very small additions of 

 extraneous matter before crystallization. 



The alteration in viscosity of the mother liquor has been suggested 

 as a reason for alteration of crystal habit. The author thinks it more 

 hkely that this alteration is due to the changes in surface tension 

 between the solid and the liquid during solidification as well as to the 

 reduction in velocity of solidification due to the impurities present. 



The " nitrogen problem " is one which has perhaps not been felt 

 very acutely in Austraha yet, as the soil has not usually been under 

 .cultivation long enough to require the same additions of manure as 

 elsewhere, but as more and more land is put under cultivation, manure, 

 natural or artificial, wiU have to be put into the ground. 



In Europe, where the dwindling of the Chili nitrates is realized 

 very intensely, special efforts have been made in recent years to obtain 

 some suitable form of artificial nitrogen compound. 



This problem is a very old one ; it was a matter of interest and 

 experiment and loss of money long before Crookes brought forward his 

 figures regarding the Avorld's wheat supply, and the world's deficiency 

 in nitrate supplies, but it has taken a long time for experiments on 

 nitrogen fixation to give satisfactory results. 



The production of synthetic nitrates, ammonia, and calcium 

 cyanamide in commercial quantities is, however, at last being carried 

 out successfully. 



For the production of synthetic nitrates, the first step is the 

 preparation of nitric oxide, for which equal volumes of nitrogen and 

 oxygen are heated by electrical means to about 2,700° C, when a small 

 proportion of nitric oxide is obtained. This gas mixture is then 

 rapidly cooled to prevent the splitting up of the nitric oxide as far as 

 possible. The nitric oxide is next converted into nitrogen peroxide 

 at a low temperature but under increased pressure, and the nitrogen 

 peroxide absorbed by alkalies. At each stage of the process the laws 

 of chemical dynamics have been brought to bear with success. 



Several plants for the production of nitrates are now working in 

 Sweden and Norway, one in South Carolina (U.S.A.), whilst others 

 are in course of erection in Germany and Switzerland. 



Calcium nitrate is the usua Initrate prepared. Lime is cheap, and 

 many experiments show that calcium nitrate is quite as good if not 

 superior to sodium nitrate as a manure. Calcium nitrate is, however, 

 more deliquescent than sodium nitrate, and it is found impracticable 



