EXPEItlMENTS OX POTATOES WITH DIFFERENT MANURES. 293 



In plants there exist certain compounds which contain nitro- 

 gen, and these may be divided into two classes : the coagulable 

 (capable of curdling) and the uncoagulable. These in the potatoes 

 were estimated in duplicate, and by two processes, viz., the 

 precipitation by carbolic acid, and the combustion with soda- 

 lime. By the first process is obtained the true amount of the 

 coagulable nitrogen compounds, called albuminoids or flesh- 

 formers, and by the latter the whole of the nitrogenous matters, 

 which are generally considered as albuminoids or flesh-formers, 

 but are in reality a mixture of the true albuminoids, with other 

 nitrogenous substances, such as solanine, &c., that are not at 

 present considered to be of any feeding value. 



I have, therefore, inserted in the table of analyses these 

 so-called " albuminoids," as distinct from the amount of the true 

 albuminoids ; I have also added the amount of nitrogen as 

 obtained by the two processes, for the albuminoids are only 

 calculated by multiplying the quantity of nitrogen, which 

 analyses show them to contain, by 6-33. The difference between 

 the two figures representing the nitrogen, as obtained by the two 

 analytical methods, may be considered as the measure of nitro- 

 genous matters present in the potato in forms other than coagu- 

 lable albuminoids, and these may be termed " amides." Fibre 

 was estimated by the " acid and alkali " process, being generally 

 done in duplicate ; the " fat, &c.," being in so small a quantity 

 and of little importance was calculated by " difference." 



Table V. shows the composition of each of the various crops, 

 as well as the amount of manure applied in each individual 

 case ; and for greater convenience of reference the mean of the 

 specific gravity determinations are placed side by side in the 

 subjoined table with the percentage of starch. 



Table VI. Showing Sioecific Gravity and Percentage of Starch. 



No relationship seems to exist between the specific gravity of 

 the tubers, and the percentage of starcli. Attempts to estimate 

 the amount of dry matter and starcli, by the aid of the tables 

 published by Heidepriem {Lancho. Vo's. Stat., xx.) * were fruit- 

 less, as the results were far from the truth, and therefore unre- 

 liable ; as, for example, tubers of specific gravity 1-127 should 

 * See also Fresenius, Jmir. Chcm. Soc, 1881, p. 932. 



