36 ANALYSIS OF PLANTS. 



the whole of the phosphoric acid is obtained at once and separately. If it is suspected, 

 however, that we do not obtain all the phosphates or phosphoric acid, we adopt the 

 separate method with another quantity of ash, using for this purpose a weighed portion of 

 iron dissolved in nitric acid. By this method, all the phosphoric acid is obtained in com- 

 bination with peroxide of iron. 



By the method I have pursued with the phosphates, a more satisfactory result is obtained. 

 We know not only what parts and organs contain the most phosphates, but also with what 

 bases they are in combination. 



The ash always contains organic matter. In almost every result we find it : it is, how- 

 ever, the most troublesome in the phosphates, and it has been suspected that it decomposes 

 phosphoric acid;, and that a loss ensues when strongly ignited. Whether there is a loss of 

 potash in burning the vegetable, is not as yet well determined. The organic matter is 

 supposed to exist as an organic salt of lime, magnesia, and perhaps potash. It seems im- 

 practicable to remove it,- and it is quite abundant in the best or whitest ash which can be 

 obtained. For a manure, ashes are so much the better for the organic matter : it is quite 

 soluble in water, and its amount is obtained from the watery solution ; the whole product 

 being perfectly dried and weighed, and afterwards ignited till it is entirely consumed, it is 

 again weighed, and the loss is organic matter. 



It is hardly necessary to say that the chlorine is Calculated from the chloride of silver, 

 and the sulphuric acid from (he chloride of barium. The proportions were obtained by 

 taking 100 grs. (usually) of the substance, drying in a water bath, and then burning it in 

 a platina or porcelain capsule. 



Organic analysis^ as detailed in the following paragraphs, consists in the separation of the 

 proximate elements, as starch, albumen, casein, dextrine, etc. The mode is sufficiently 

 simple, but seems to be liable to some variations in consequence of the easy decomposition 

 of some of these bodies on exposure to the atmosphere. 



The potato is first washed, and then dried, or freed from the outside water. It is then 

 sliced longitudinally, and laid upon blotting paper a moment in order to absorb the exuded 

 moisture. Two or three hunched grains are then weighed, when it is immediately grated 

 carefully, and so as to be free from unbroken pieces of the potato. The grated portion is 

 allowed to subside in pure water, after passing through fine muslin. The starch collects 

 at the bottom ; and the fibre, after thorough washing, remains upon the muslin filter. The 

 supernatant liquor is drawn off from the starch by a syphon. The small quantity of fluid 

 remaining upon the starch, and the starch itself, is thrown upon a filter and washed again, 

 and the filtrate is added to the liquid drawn off by the syphon. The liquid is often quite 

 bulky : it may, however, be divided into two equal parts ; one for albumen, and the other 

 for casein. The first is boiled or heated to above 160° Fahr., when the albumen separates 

 in thin coagulated masses, and subsides in the conrse of twelve hours. This is filtered 

 upon a prepared filter, and dried in a water bath preparatory to weighing. The casein is 

 precipitated from the other half by acetic acid. The liquid, after complete subdivision, is 

 drawn off with a syphon, and filtered, dried and weighed. The dextrine may be obtained 



