As the alkaline chlorides are, moreover, not 
completely fixed at a red heat, some loss is not 
unfrequently sustained by a long continued 
_ ignition. We may dispense with the employ- 
_ ment of nitric acid and avoid loss from volati- 
lization by shortening the period during which 
a high temperature is kept up, and simply char- 
__ Ting the mass at a low red heat so as to destroy 
all organic matter; the black residuum is then 
digested in water, by which the alkaline salts 
dissolve, and after well washing, a little weak 
nitric acid is employed to remove the earthy 
compounds: charcoal alone remains undis- 
solved. By evaporation of the solutions the 
amount of saline matter is ascertained. 
Filtration may be performed on good white 
unsized blotting paper cut of a size to drop 
completely within the funnel; before pouring 
in the fluid to be cleared, the filter should be 
_ moistened, if the solution be aqueous, with 
water; if alcoholic or ethereal, with a few drops 
of alcohol or ether, as the case may be. In 
order to ascertain the quantity of dry residue, 
’ the preferable plan is to employ two filters pre- 
_ viously counterpoised one against the other, 
and to insert one into the other; the excess of 
weight the inner filter shews when the filtra- 
_ tion is complete, after both have been carefully 
dried on the water-bath, will furnish the quan- 
_ tity of solid matter. To render the filtration 
more rapid, the apex of the outer filter may be 
cut off so as to leave only one thickness of 
_ paper at the point. “Occasionally we may 
_ weigh the filter itself and mark its weight in 
pencil upon it; the objection to this plan con- 
| Sists in the difficulty of obtaining the paper 
always at the same point of dryness. It should 
| be first dried at :212°F., placed in a light covered 
_ capsule over sulphuric acid, and allowed to 
_ cool, then weighed whilst covered from the air. 
| The same care must be observed on again 
weighing it with the precipitate. Of course 
' in washing an organic precipitate, the same 
_ precautions will be required as when pro- 
ceeding with the analysis of a-mineral. The 
‘stream of washing liquid should be speci- 
| ally directed to the edges of the filter, which 
_ may be known to be sufficiently washed, when 
by the evaporation of a drop of the liquid 
‘which passes through on a slip of glass, no 
perceptible stain is produced. 
_ Whenever decantation, or pouring off from 
the sediment, can be. substituted (as it very 
frequently may in alcoholic and ethereal di- 
gestions) for filtration, it is to be preferred, as 
‘some loss is unavoidably occasioned by every 
filtration; whereas by decantation the preci- 
ee may be dried in the vessel, and if this 
have been previously counterpoised we can 
ascertain the weight of adhering matter with 
‘great exactness. By this method the precipitate 
may be as perfectly washed as when filtration 
is adopted ; the fluid may be poured off very 
close to the solid matter, which may again be 
\diffused through a fresh portion of washing 
jfluid, again allowed to subside, and the wash- 
jing repeated as often as may be necessary. In 
pouring a fluid from one vessel to another, loss 
jis avoided by moistening a glass rod in the 
ORGANIC ANALYSIS. 
795 
liquid, bringing it into contact with the lip of the 
glass or basin, and pouring the liquid down this 
rod, which is not removed until the side of the 
vessel is nearly restored to the vertical pusition ; 
by observing this precaution we escape the risk 
of losing any portion from its running down 
the outside of the vessel. The drops adhering 
to the rod are washed into the rest of the 
solution. 
The animal substances that we have to ex- 
amine naturally arrange themselves into fluids 
and solids, and as this division is convenient 
in a practical point of view, I shall here adopt 
it, beginning with those presented to us ina 
fluid state. 
In order to fix some definite limit to our 
enquiries, those principles only will here be 
noticed, which, from the frequency of their 
occurrence or their importance as constituents 
or products of the living frame, are most likely 
to be the special objects of attention to the 
physician and pathologist. In this number 
among the fluid products I shall enumerate 
fibrin, albumen, casein, fatty matters, urea, 
sugar, the uric, urobenzoic, lactic, and oxalic 
acids, mentioning a few other compounds, as 
ptyalin, sulphocyanic acid, &c. &c., when 
describing the general plan of analysing the 
secretions in which they most commonly 
occur. 
A. ANALYSIS OF ANIMAL FLUIDS. 
» When an animal fluid is presented for ana- 
lysis, it is necessary in the first place to acquire 
a knowledge of the ingredients which enter 
into its composition in order to be able to 
decide upon the best method of ascertaining 
their proportions. The means of determining 
the nature and quantity of the organic con- 
stituents will be first described, leaving the. 
saline matters for a subsequent section. 
1. For the organic constituents. 
It is possible that all the principles just 
enumerated may occur together; this, however, 
will very rarely happen unless we have to 
examine the contents of the stomach, when a 
still more ‘heterogeneous mass may be pre- 
sented to us. 
Having, where practicable, taken the specific 
gravity of the liquid in order to acquire an 
idea of its degree of concentration, we place 
a portion under the microscope, and are thus 
enabled at once to decide upon the presence 
of blood globules, pus globules, fatty or oily 
matters in suspension, the debris of tissues, 
crystals of various substances, as uric acid, 
cholesterin, &c., and may then pass to tests 
purely chemical for its 
Qualitative analysis. 
a. By allowing the liquid to stand at rest for 
a few hours, we at once determine the presence 
of fibrin, which coagulates and separates spon- 
taneously, at the same time enveloping the 
red globules and suspended particles in its 
meshes. 
6. The clear liquid is heated to boiling; if 
albumen be present it coagulates, unless the 
solution bealkaline, when the addition of a few 
drops of nitric acid causes an immediate curd- 
ling. A drop or two of acetic acid added to 
