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. Ify 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 the 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 hundred 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 course 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 
