5. Of the saliva.
The saliva is not often the object of analysis; when it is, it may be proceeded with as in the following instance, in which healthy saliva was examined. It was obtained several hours after taking food. It had a sp. gr. of 1001.5, was slightly alkaline, restoring the colour of red d ened litmus paper ; and was ropy and opalescent.
(a) 111 grs. evaporated to dryness in a pla tinum capsule and incinemted, left 0.22 g-rs. of ash.
111 : 1000 : : 0.22 : x (= 1.98) saline mat ter per 1000.
(b) 500 grs. evaporated by a water-bath left 2.51 grs.
500 : 1000 : : 2.51 : x (= 5.02) total solids. 5.02 - 1.98 = 3.04 organic matter.
1000 - 5,02 = 994.98 total quantity of water.
(c) The dry residue was digested in ether ; the ethereal solution decanted and evaporated left 0.03 grs. of an oily matter with a strong peculiar odour. It contained a trace of sulpho cyanide of potassium, as was shewn by the red colour struck by a very dilute solution of ses quichloride of iron.
500 : 1000 : : 0.03 : (= 0.06) fatty odorous matter with traces of sulpho cyanide potassium.
(d) The residue undissolved by ether was treated with boiling alcohol; the solution de moted and evaporated left 0.61 of a crystalline yellowish deliquescent salt, in which the pre sence of sulphocyanide of potassium was proved ; 1st, by its striking a blood-red liquid with a very dilute solution of sesquichloride of iron ; and 2ndly, this solution, according to Dr. Percy's suggestion, was acidulated with hydrochloric acid, and a fragment of zinc dropped in. Immediate effervescence ensued with a strong odour of sulphuretted hydrogen due to the decomposition oldie sulphocyanide. Its acidulated aqueous solution gave no preci pitate with nitrate of baryta ; but after a small portion of the alcoholic extract had been inci nerated and the residue dissolved in water feebly acidulated with nitric acid, abundant precipitation was manifest on adding a solution of chloride of barium; during incinemtiou the sulphocyanide had been decomposed and the sulphur, by absorbing oxygen, converted into sulphuric acid.
500 : 1000 : : 0.61 : (= 1.22) akoholic extract.
(e) The residue left undissolved by alcohol was treated with water and thrown upon a weighed filter; the insoluble portion amounted to 0.68 : it consisted of mucus, debris of epi
theliurn, &c.
500 : 1000 : : 0.68 : (= 1.36) mucus.
(f) The filtered solution contained traces of albuminous matter (mucus) held in solution by the soda. This was precipitated by exact neu tralization withaceticacid,evaporated todryness, redissolved, and again filtered. This aqueous liquid contained the ptyalin, or peculiar sali vary matter, and a certain proportion of watery extract so called. Ptyalin has never yet been obtained in a state of purity. It always contains chlorides and phosphates mixed with it. The so lution was mixed with twice its bulk of alcohol, by which the ptyalin in company with some watery extract was precipitated. Its solution, when redissolved in water, gave precipitates with acetate and triacetate of lead, infusion of galls, and nitrate of silver, but none with cor rosive sublimate, sesquichloride of iron, or ferrocyanide of potassium, either alone or after the addition of acetic acid. Each time it is evaporated to dryness a small portion remains behind in an insoluble form. Deducting the ethereal and alcoholic extract, and mucus, 5.02 -(1.22 0.06 +1.36 (e))= 2.38 re presents the ptyalin and watery extract per 1000.
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 larnp. If the metal were there, it would sublime and condense as a dew of metallic globules on the cool part of the tube.
II.—Ill•rimATE 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 rnatters 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.