ORGANIC ANALYSIS. 



813 



This specimen of healthy saliva therefore 

 contained, 



Water 994.98 



("Fatty and odorous 



matter 0.06 



Alcoholic extract 



and salts 1.22 



Mucus and epithe- 

 lium 1.36 



Ptyalin, watery ex- ^ 

 tract, salts and > 2.38 

 traces of mucus j 



Organic matter, 



3.04. 

 Fixed salts, 1.98. 



1000.00 



If mercury were sought for, the best plan 

 would be to mix a little nitric acid with the sa- 

 liva, evaporate to dryness, mingle the dry mass 

 with well-dried carbonate of soda, to place the 

 mixture in a fine glass tube sealed at one end, 

 and apply the heat of a spirit lamp. If the 

 metal were there, it would sublime and condense 

 as a dew of metallic globules on the cool part 

 of the tube. 



II. ULTIMATE ANALYSIS. 



Organic bodies consist principally of carbon, 

 hydrogen, oxygen, and nitrogen, with occa- 

 sionally small quantities of sulphur, phos- 

 phorus, and various metallic, earthy, and saline 

 matters in minute proportions. In cases where 

 the four first elements only are present, the 

 analysis is comparatively easy; and if, as some- 

 times occurs, the substance to be analysed is 

 capable of assuming a crystalline form, its 

 purification is a matter of little difficulty. 

 When, however, saline compounds enter es- 

 sentially into its constitution, as in most animal 

 principles, crystallization is never found to take 

 place. 



This general absence of crystalline form in 

 animal principles, and the consequent difficulty 

 of ascertaining that they are free from all mois- 

 ture, which does not chemically enter into their 

 constitution, have, by rendering us uncertain 

 of the purity of the substances analysed, mainly 

 contributed to the slow and uncertain progress 

 of this department of chemistry, and have 

 given rise to the numerous 

 contradictory statements 

 with which it abounds. By 

 multiplied researches and 

 experiments we are, how- 

 ever, at length arriving at 

 results on the accuracy of 

 which tolerable confidence 

 may be placed. 



The determination of the 

 four elements, carbon, hy- 

 drogen, oxygen, and nitro- 

 gen, as they constitute the 

 bulk of most organic sub- 

 stances, is that part of the 

 process which now claims 

 our attention. It is to Gay 

 Lussac and Thenard that we 

 are indebted for the funda- 

 mental principle that 

 gulates our 



has subsequently been modified and improved 

 by many chemists, especially by Berzelius, 

 Prout, and Liebig, and in the hands of the lat- 

 ter eminent philosopher it has acquired a de- 

 gree of facility and accuracy hitherto unap- 

 proached in any other department of analytical 

 research. 



Our object being to determine the relative 

 proportion in which each of the ultimate ele- 

 ments exists, it becomes necessary to the success 

 of any analytical process that we should pro- 

 cure them in the form of definite compounds 

 that can easily be collected ; and it has been 

 found most convenient, by supplying the sub- 

 stance to be analysed with a sufficient quantity 

 of oxygen, to convert the carbon into carbonic 

 acid, which may be absorbed by polassa and 

 weighed, and the hydrogen into water, which 

 may likewise, by passing over a substance that 

 has a powerful attraction for it. such as chloride 

 of calcium or sulphuric acid, be collected 

 and weighed, whilst the nitrogen escapes 

 as gas, which is collected over mercury and 

 measured. 



In cases where nitrogen is present, it has re- 

 cently been proposed to heat the substance to be 

 analysed along with hydrate of soda or potash ; 

 all the nitrogen is thus converted into ammonia, 

 in which form, like carbonic acid and water, it 

 admits of being weighed. By calculation it is 

 easy to find the weight of the carbon, hydrogen, 

 and nitrogen respectively contained in the car- 

 bonic acid, water, and ammonia collected. Car- 

 bonic acid contains three-elevenths of its weight 

 of carbon; water, one-ninth of hydrogen, and 

 ammonia fourteen-seventeenths of nitrogen. 

 When by incineration of a portion of the mass 

 the proportion of saline matter has been deter- 

 mined, the quantity of oxygen the substance 

 contains may be known by deducting the united 

 weight of the carbon, hydrogen, nitrogen, and 

 salts from the total weight of the body ana- 

 lysed ; the deficiency (supposing sulphur and 

 phosphorus not to have been present) is oxygen. 



Scrupulous attention to the purity of the 

 matter submitted to analysis is of course of 

 primary importance, a very slight admixture 



Fig. 429. 



A 



Apparatus for desiccation of organic substances. 



tube containing chloride of calcium resting on the support B j 

 c, bent tube containing the matter to be dried and plunged in the bath 



n n a rp 



dl , D ; d, d, caoutchouc connectors ; E, vessel containing water, which 6ows 



operations. Ihe out gradually by the stop-cock/ to maintain a current of air through the 



process proposed by them apparatus. 



