Determination of the Lime by a graduated solution of We give this method after Neubauer, who obtained accurate results by it. The oxalate of lime obtained as above is transformed into carbonate by the aid of heat, and dissolved in hydrochloric acid of known strength. The amount of acid not neutralized is then ascertained by a graduated solution of soda. Preparation of the standard solution of hydrochloric acid.— One cubic centimètre of this acid is exactly to neutralize 10 milligrammes of lime, or CaO. One litre of the acid would therefore have to correspond to 10 grammes of CaO or 18.93 grammes of carbonate of soda. A small quantity, say about one gramme, of carbonate of soda, after having been made red hot and allowed to cool again, is weighed and dissolved in water. Some tincture of litmus is now added to colour the solution fairly blue. It is then made boiling hot, and the dilute hydrochloric acid is added from a burette, until the blue colour of the solution has given way to a light-red colour, resembling the red of onion-peel. It is well to keep the fluid at the boiling point during the addition of the acid, in order to remove all carbonic acid as quickly as possible, which latter, by giving the fluid a colour of red wine, would not permit of the transition of the blue colour into red being accurately perceived. Suppose we have found that one litre of the dilute hydrochloric acid employed corresponds to 41.6 grammes of carbonate of soda, then 18.9 grammes of the latter will exactly require 4570 c.c. of the acid for saturation. We take therefore 457.0 c.c. of the acid, whereby we obtain 10000 c.c. of standard solution, of which 10 c.c. corresponds to 0.0189 grammes of carbonate of soda (NaO, CO2), or 0·010 grammes of CaO. The correctness of the solution is to be checked by several experiments. Preparation of the solution of soda to correspond to the former solution.-Of this solution 10 c.c. must exactly neutralize 10 c.c. of the solution of hydrochloric acid, so that after the addition of the last drop of the 10 c.c. of the solution of soda to the acid, the red colour of the latter (by litmus) is changing to blue. To observe the colour accurately, it is well to take care that the solution of soda be free from carbonic acid. To 10 c.c. of the standard solution of hydrochloric acid, coloured red by means of tincture of litmus, we add the dilute solution of soda, which is to be graduated, from a burette, until the red colour has changed to blue. Suppose we have used, for 100 c.c. of the standard solution of hydrochloric acid, 80 c.c. of the solution of soda, then we add to 8000 c.c. of solution of soda, and thus we obtain 1000'0 c.c. of solution of soda, of which 100 c.c. must exactly neutralize 100 c.c. of the standard solution of hydrochloric acid. The fluids applied. The oxalate of lime, obtained from a known quantity of urine, say 100 c.c., in the manner described, is exposed to red heat, and transformed into carbonate of lime and quicklime. It is then transferred into a balloon with the aid of some water; 10 c.c. of the standard acid solution are then added, and the solution thus obtained is heated until all carbonic acid has been driven away. The solution is then coloured red by means of litmus. The standard solution of soda is now added until the red colour has changed to blue. The number of cubic centimètres of the solution of soda subtracted from the 100 c.c. of standard acid leaves the number of cubic centimètres neutralized by the lime, each cubic centimètre corresponding to 10 milligrammes of lime. By multiplying by 10 the number of cubic centimètres of standard acid neutralized by lime, we obtain the per centage of lime contained in the urine when 100 c.c. of it have been taken for analysis. Determination of Magnesia by means of volumetrical analysis of its Phosphoric Acid. For this purpose the magnesia is isolated in the form of triple phosphate, and dissolved in acetic acid. In this solution the phosphoric acid is now determined by means of the graduated solution of chloride of iron. This method does not give very accurate results. Deposits of Earthy Phosphates. As a rule, deposits of earthy phosphates can exist only in urine exerting an alkaline reaction upon test-paper. The presentation of an acid reaction by urine, therefore, excludes the possibility of the occurrence of these deposits. There is only one (questionable) case in which a deposit of an earthy phosphate is compatible with an acid reaction of the urine; namely, when urine containing little or no free acid exerts an acid reaction from the presence of chloride of ammonium. In this case a deposit of phosphate of magnesia may perhaps exist; for this salt is little or not soluble in chloride of ammonium. But phosphate of lime is so soluble in the latter salt, that it could not exist as a deposit so long as any acidity of the chloride of ammonium is not neutralized. The observations which are said to have been made of urine having an acid reaction, and yet containing a permanent deposit of phosphates, if they cannot be explained in the way just detailed, must be considered as fallacious. They are contrary to the commonest law of chemistry. I have made some observations, which may serve to explain the manner in which such statements have come to be called observations. Clear acid urine was allowed to stand for three hours, when a pellicle of phosphates was observed on the surface. Blue test-paper, immersed an inch deep into the fluid, on being withdrawn had become red. Another piece of the blue testpaper was now laid flat upon the surface of the fluid, when no reaction took place. The upper stratum of the urine had evidently become alkaline under the influence of the air, while the lower strata had retained their acidity. Urine may be acid for a short time and yet contain a deposit of phosphates; or it may contain a deposit of phosphates for a short time, and yet remain acid, under the following circumstances. If to acid urine in the bladder a secretion of alkaline urine be superadded, and the person remain very quiet, the lower strata of the urine in the bladder may be alkaline and contain a deposit, while the upper remain acid. Of course this may vary according to the different densities of the two secretions. My explanation is based upon a case in which urine was discharged acid, and yet thick from the presence of phosphates. But the upper strata of the urine soon became quite clear, and a little cloud at the bottom of the vessel dissolved on agitation. We have already seen that an alkaline reaction of the urine may be due to various causes, and have distinguished between alkaline reaction from fixed alkalies, derived from the blood, and that which is due to the presence of ammonia from decomposition of urca. The deposits of earths taking place 'Dr. G. Bird, Urin. Dep.,' p. 260, § 261. under the neutralizing influence of both alkalies are identical as regards phosphate of lime, different as regards phosphate of magnesia. For the latter is deposited by fixed alkali, as PO + 3MgO + 5HO, while in the presence of ammonia it takes up one equivalent of this base and water of crystallization, and appears as PO, + 2MgO + NH ̧0 + 12Aq. A deposit containing this latter salt is therefore due to the presence of ammonia from decomposed urea. If the acid, by means of which phosphate of lime is kept in solution in the urine, be a volatile one, namely, carbonic acid, as was observed in one case, which will be quoted in another page, the spontaneous or intentional evaporation of the acid may cause a deposit of lime to appear. Deposits of Phosphate of Lime. Physical characters.-Deposits of phosphate of lime, as usually occurring in the urine and mixed with magnesia, are always white, amorphous, under the microscope appearing in granules, sometimes of a greenish tinge, which exert a refracting action upon light. Crystallized deposits of this substance have not been observed; but it is more than doubtful whether it does not enter into the chemical composition, or is an admixture of some crystalline sediments. Crystallization.-Phosphate of lime may be obtained in a crystalline state from its solution in acetic acid. When this solution is allowed to stand some time, the phosphate has a great inclination to fall down from this solution in a crystalline state, particularly when the mixture is warmed a little, and when the phosphate is prevalent. By precipitation of phosphate of soda with chloride of calcium, an amorphous gelatinous deposit of phosphate of lime is obtained. This after standing some days becomes transparent, like solution of gum. When a sunbeam is now allowed to fall on the precipitate, myriads of glistening crystalline points may be observed disseminated through the amorphous part of the deposit. Under the microscope these crystals appear as delicate, thin, clino-rhombic plates, very much like the crystals of oxalate of urea.1 Chemical diagnosis of deposits of phosphate of lime.-The occurrence in neutral or alkaline urine only is the first point to be observed. The deposit is insoluble in water, For a perfect crystallographical description, see Schmidt, C., Krystallonomische Untersuchungen,' 1846, p. 58. soluble in weak acids, such as acetic acid, and is again precipitated from the acid solution in its original form by ammonia. From the acetic acid solution oxalate of ammonia throws down oxalate of lime. This latter test distinguishes it from the phosphate of magnesia, with which it is always mixed. Phosphate of lime alone does not easily fuse before the flame of the blowpipe. When diffused in urine, the deposit appears like a dense cloud of mucus, from which it is not easily distinguished, because it is mostly mixed with it, and resembles it in colour. When it appears in urine on the application of heat, its resolution on cooling, or by the addition of an acid, distinguishes it from albumen. Deposits of Ammonio-phosphate of Magnesia. Physical characters.-Deposits of this substance always occur in well defined crystals in ammoniacal urine. No substance commonly occurring in the urine, and being insoluble in water, presents the same glistening glass-like appear ance. But Form of crystallization.-The triple phosphate crystallizes in the rhombic system. The form most commonly met with is the vertical prism, combined with terminal planes derived from macro- and brachy-diagonal horizontal prisms. Some of these forms1 resemble hippuric acid very much. there is this crystallographical distinction between them, that on crystals of hippuric acid we frequently observe planes derived from the rhombic octahedron, which in triple phosphate are scarcely ever met with. See plate III, fig. 2. Not rarely these crystals have a tendency to cross each other at regular angles. This is best seen in crystals obtained from blood. The latter serve to explain other forms observed in the urine, namely, the stellæ,2 which are not merely acicular prisms cohering at one end, but prisms crossed at regular and symmetrical intervals. They very much resemble crystals of snow. These latter, however, being prisms of the hexagonal or rhombohedral system, cross at equal angles (of one sixth of the circle each), since the triple phosphate crystals cross at angles of which only four are equal, the other two being equal to each other. 1 Vide Schmidt, loc. cit., p. 48. |