EXPERIMENTS ON POTATOES WITH DIFFEPtENT MANURES. 295 



superphosphates were used alone. All other additions appear to 

 have acted prejudicially "on the quality of the potato, except- 

 ing, however, when undissolved phosphate was employed, and 

 then we find that additions of other manures were beneficial 



The reduction of the amount of starch was produced by the 

 sulphate of ammonia, but not to so great an extent as when it 

 was in combination with kainit, which last admixture is evidently 

 most unsatisfactory, when the aim of the agriculturist is to pro- 

 duce a starchy potato ; and in these experiments we find that 

 those tubers which grew on the unmanured plots contained as 

 much starch as if they had been treated with ammonia and 

 kainit.* 



" Potashes " and ammonia do not seem to be quite as preju- 

 dicial as the kainit, but the slight gain in starch over the 

 unmanured plot (24) is not commensurate with the additional 

 outlay, unless the yield be large. As the kainit w^as put in with 

 the other manures, and not as Volcker recommends, at an earlier 

 period, it is possible that the percentage of starch might have 

 been raised, if this plan had been followed. As soon as this 

 deleterious effect of kainit was perceived, we determined that 

 in the succeeding set of experiments (which were commenced 

 June 4, 1881), we would employ such manures as should aid us 

 in determinintr wdiich ini^redient it was that caused this reduc- 

 tion in starch, whether it was the large amount of sulphuric acid 

 added in the kainit and sulphate of ammonia, or whether it was 

 the magnesia. However, a paper by A. Meyer {Landu\ Ver. 

 Stat, xxvi. 77, and Jou7\ Chem. Soc, 1881, p. 459) has in part 

 answered our inquiries, for it is there shown that bases com- 

 bined with mineral acids (such as sulphuric acid), are not so 

 readily assimilated as if they had been in combination with 

 organic acids, as carbonic acid, &c., so that here we may have an 

 explanation of the efi'ect produced by " potashes " as compared 

 with that produced by the potassium in kainit. 



Effect on the amount of Nitrogen (Table V.). — Under tliis 

 heading the nitrogen present in the form of coagulable albumi- 

 noids, and that in any other form such as " amides," &c., are to 

 be considered, and not only these two separately, but the pro- 

 portion which one bears to the other. As the ordinary " soda- 

 lime " method of analysis does not give always the absolute 

 quantity of nitrogen present, the figures which represent the 

 "Total Nitrogen" must be considered only as an approximation 

 to the true quantity, therefore the difference between the two 

 "Nitrogens" whicli represents the "amides" is also but an 

 a])[>r()ximation. 



Noticing firstly the true albuminoids present, I find that the 



* Kainit and superpliospliatc alone (Plot B) In-ing, on the other liand, satis- 

 factory. 



