mn ORGANIC ANALYSIS. 
\ 
are able the quantities in which they may be 
present: this portion of the subject I shall con- 
clude with a brief sketch of the general method 
of analysing the principal secretions in the 
healthy and more ordinary morbid conditions,— 
for more ample details I must refer to the articles 
specially devoted to the history of each secretion. 
_ I shall then, in the second place, proceed with 
_ an outline of the processes best adapted to the 
_ ultimate analysis of organic bodies in general. 
if To the pathologist the first of these objects 
is the most important, and it is he alone who 
ft es the extensive facilities requisite for 
__investigating the different varieties exhibited by 
the secretions in disease, whether these varieties 
_ present themselves in the undue prevalence of 
_ one or more of the proximate principles, the 
undue deficiency of any of them, or the unu- 
_ sual occurrence of any of them among the 
secretions, or in the tissue of particular organs. 
The value of such information to the enlightened 
_ practitioner is sufficiently evident, for an accu- 
rate and ready mode of appreciating these 
_ changes not only affords him some of the most 
| unerring indications of the nature and progress 
_ of disease, but enables him likewise to appre- 
ay ciate the effects and influence of the remedial 
_ Measures that he may think it needful to adopt. 
‘To the chemist, on the other hand, belongs more 
‘appropriately the task of determining what 
Ought to be considered as really proximate prin- 
‘ciples, of insulating them in a pure state, and 
finally of ascertaining their elementary com- 
position by ultimate analysis. 
__ In every case, before proceeding to analysis, 
it is desirable, nay, in the present state of 
science almost necessary, to subject the mate- 
lal to a careful microscopic examination ; for 
although this does not of itself suffice to deter- 
mine the chemical nature of the substances 
with which we have to deal, it yet furnishes us 
vith the most important preliminary information 
ve can acquire, and is frequently, owing to 
their close chemical relationship, the only means 
ertaining what is the form of the azotised 
stituents of the body with which we have to 
do. In truth, unless a chemist be likewise in 
some degree acquainted with the resources 
pl iced at his disposal by the microscope, he is 
but half fitted for the task of organic analysis. 
For the necessary information respecting the 
inute structure of the different products of 
uimal organization, I must again refer to the 
farious articles on the subject in different parts 
is work. (See Broop, Cuyze, Mirk, 
Mucus, Pus, Satrva, Urine, &c.) 
& I,—ProximaTE aNaLysis. 
As the limits of this article preclude the pos- 
bility of my entering into detail upon the 
dinary operations of analysis, a task happily 
endered unnecessary by the excellent manuals 
€ possess on the subject, I shall limit myself 
a few remarks on processes connected more 
amediately with organic analysis. 
It is needless here to insist upon the impor- 
nce of scrupulous attention to the purity of 
e re-agents employed, as it is a precaution 
ficiently obvious. These re-agents are few 
number: sulphuric, nitric, hydrochloric (or 
793 
muriatic), and acetic\acids, solutions of potash, 
ammonia, and carbona’ ammonia, alcohol, 
and ether, constitute the most important; if to 
these we add solutions of 
Chloride barium, Acetate lead, 
Nitrate silver, Subacetate lead, 
Oxalate ammonia, | Sulphate copper, 
Phosphate soda, Sesquichloride iron, 
Ferrocyanide potas- { Bichloride platinum, 
sium, Tincture galls, 
Alum, Hydrosulphuret am-~- 
Lime water, monia, 
with a blowpipe, platinum foil, spirit-lamp, 
forceps, test-tubes and a stand for them, a few . 
watch-glasses, evaporating dishes and Florence 
flasks, a retort stand, funnels of different sizes, 
filtering paper and some lipped glasses, with 
pieces of glass rod and strips of window glass, 
we shall be tolerably well prepared for the 
operations of proximate analysis. Of course 
distilled water must always be employed in 
analytical enquiries. 
For proximate analysis scales weighing 2000 
grains and turning with th of a grain, when 
fully loaded, will be sufficient; but for ulti- 
mate analysis they should be sensible to 4},th 
of a grain when each pan carries 1000 grains. 
When the weight of a dry residue is to be 
ascertained, the object is attained with most 
accuracy by first counterpoising the vessel when 
empty, and then determining the increase of 
weight after the desiccation is completed. 
The desiccation of all organic substances is 
best performed, where practicable, in the ex- 
hausted receiver of an air-pump, over sulphuric 
acid, by Leslie’s process: a flat dish of oil of 
vitriol is placed on the plate of the pump, and 
the substance to be dried supported above it 
in a basin by a triangular framework of wire; 
the air is exhausted, and care taken to maintain 
a good vacuum ; the residue thus procured is 
always much purer and whiter than that fur- 
nished by any other means, but it is a tedious 
and circuitops process, and requires ten days or 
a fortnight for its completion. Upon this ac- 
count, and for other reasons, this method can- 
not generally be adopted. The plan which, ° 
next to it, presents the fewest objections, con- 
sists in evaporating by a steam or water heat, 
so that the temperature can never exceed 212° 
Fahr. Various methods may be resorted to 
for effecting this object; by placing one basin 
within another containing water, an extempo- 
raneous bath is procured ; but the end is more 
conveniently attained by the employment of a 
shallow box of copper, zinc, or tin plate, in the 
top of which are half-a-dozen circular apertures 
of different sizes with projecting vertical rims, 
upon which lids may be fitted when not in use; 
any vessel to be heated is placed over one of 
these apertures, and the temperature maintained 
by oil, gas, or sand heat. 
Perfect desiccation is essential to accuracy, 
and from the destructible nature of some or- 
ganic compounds, especially under the com- 
bined influences of atmospheric oxygen and an 
elevated temperature, it is dangerous to effect it 
by heat and difficult by any other means. In 
some delicate experiments the following plan, 
