ORGANIC ANALYSIS. 



793 



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. 



To the pathologist the first of these objects 

 is the most important, and it is he alone who 

 possesses 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- 

 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- 

 rial 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 

 with the most important preliminary information 

 we can acquire, and is frequently, owing to 

 their close chemical relationship, the only means 

 of ascertaining what is the form of the azotised 

 constituents of the body with which we have to 

 do. In truth, unless a chemist be likewise in 

 some degree acquainted with the resources 

 placed at his disposal by the microscope, he is 

 but half fitted for the task of organic analysis. 



For the necessary information respecting the 

 minute structure of the different products of 

 animal organization, I must again refer to the 

 various articles on the subject in different parts 

 of this work. (See BLOOD, CHYLE, MILK, 

 Mucus, Pus, SALIVA, URINE, &c.) 

 I. PROXIMATE ANALYSIS. 



As the limits of this article preclude the pos- 

 sibility of my entering into detail upon the 

 ordinary operations of analysis, a task happily 

 rendered unnecessary by the excellent manuals 

 we possess on the subject, I shall limit myself 

 to a few remarks on processes connected more 

 immediately with organic analysis. 



It is needless here to insist upon the impor- 

 tance of scrupulous attention to the purity of 

 the re-agents employed, as it is a precaution 

 sufficiently obvious. These re-agents are few 

 in number : sulphuric, nitric, hydrochloric 



muriatic), and acetic acids, solutions of potash, 

 ammonia, and carbonate of ammonia, alcohol, 

 and ether, constitute the most important; if to 

 these we add solutions of 



Acetate lead, 

 Subacetate lead, 

 Sulphate copper, 

 Sesquichloride iron, 

 Bichloride platinum, 

 Tincture galls, 

 Ilydrosulphuret am- 

 monia, 



Chloride barium, 



Nitrate silver, 



Oxalate ammonia, 



Phosphate soda, 



Ferrocyanide potas- 

 sium, 



Alum, 



Lime water, 

 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 1 i g 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 di xiccation 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 circuitous 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, 



