CRYSTALLINE COMPONENTS 63 



n = 1-99 X 12-42 X 7-37/155 X 1-648 = 8-82. Hence it appears that the tetragonal unit 

 cell contains approximately 9CaC,04. i JH2O. The crystal-structure of oxalic acid and 

 many oxalates have now been worked by W. H. Zachariasen (1934) and S. B. Hendricks 

 (1935). In all of them the C2O4 group has constant shape and dimensions. Both the 

 unit-cell dimensions and the space-group of the renal calculi crystals would lead us to 

 expect an even, not an odd number of C2O4 groups per unit cell. It is difficult in the 

 face of the X-ray evidence to imagine how more than eight C2O4 groups can be accom- 

 modated. Therefore either the observed specific gravity or the chemical composition or 

 both are inconsistent with the X-ray data. 



In the meantime it had been found that the powdery material forming the matrix of 

 the renal calculi crystals effervesces when dissolved in dilute acids and gives a reaction 

 for phosphate. This is also true of the crystals themselves, probably due to fine-grained 

 inclusions of the matrix. Moreover, a small residue of organic tissue remains after 

 solution of a calculus crystal or matrix in acid. The first analysis on the white crystals 

 must therefore be rejected, since it is clear that the presence of organic matter would 

 disturb the permanganate titration and give too high a value for the oxalate content. 

 The phosphate content of the crystals is also appreciable and possibly due to admixture 

 of the calcium oxalate salt with dahllite, 3Ca3(P04)2.CaC03. The latter constituent is 

 extremely fine-grained and attempts to separate sufficient from the crystals for optical 

 tests or from the matrix for chemical analysis proved unsuccessful. 



Two further chemical analyses were now made on pale-brown crystals, sp. gr. 1-99, 

 from the unnumbered calculus. It is impossible to determine the water content directly 

 since the crystals when dried at 270^ C. still contain about 6 per cent H,0 and if the 

 temperature is raised above 270° C. the oxalate begins to decompose. Nor can the 

 oxalate be determined by titration with potassium permanganate owing to interference 

 by included organic tissue. Accordingly the powdered crystals (io-o6 mg. for analysis 

 I, 14- 11 5 mg. for analysis 2) were weighed into a small crucible, dried at 270° C, heated 

 at 580'' C. to decompose the oxalate, reweighed and then ignited at 950° C. The residue 

 was weighed and the phosphate content determined as ammonium phosphomolybdate. 

 The ignitions at 580 and 950° C. correspond to the following reactions: 



{a) Hydrated calcium oxalate + dahllite ^2^' CaCOa + Ca3(P04)2 + CO + HO^. 

 Loss of weight due to evolution of CO + H2O. 



ib) CaCOg + Ca3(P04)2 !!!!^ CaO + Ca3(P04)2 + COg. 

 Loss of weight due to evolution of CO2 . 



Table I gives the results of the two analyses, together with the recalculated figures 

 allowing for deduction of dahllite. Table II shows that the two recalculated analyses 

 correspond approximately to CaC204.2H20. The observed specific gravity 1-99 should 

 also be corrected for a content of 4 per cent dahllite, see Table I. Assuming a specific 

 gravity 3-1 for the latter constituent, the corrected value for the renal calculi cn,'stals 

 is 1-94. The specific gravity calculated from the X-ray data and assuming that the tetra- 

 gonal unit cell contains 8CaC204.2H20 is 1-91. The chemical and X-ray data are there- 



