CRYSTALLINE COMPONENTS 6i 



were also taken with a square edge vertical (Plate II, fig. 3), with a diagonal vertical and 

 also about the c axis [001] (Plate II, fig. 4). The smallest tetragonal unit cell which can 

 be assigned to the crystals on the basis of these photographs has the dimensions a 12-40, 

 c 7-37 ± 0-02 A. The indices of the pyramid faces are therefore {loi}. The calculated 

 axial ratio is c : <? = 0-594 • ^ corresponding to a calculated cr angle = 30° 42J', in close 

 agreement with the goniometric value, 30° 35'. Rotation and oscillation photographs 

 about the [100] axis were then indexed and the unit cell found to possess the symmetry 

 of the space-group C\j^ = I 4/m. 



The optical and crystallographic data so far obtained show that the crystals cannot be 

 identified with any known tetragonal mineral. Fortunately, determinative data for all 

 organic and inorganic substances known to possess tetragonal symmetry have recently 

 been compiled by Hey,^ and independently by J. D. H. Donnay and J. Melon (1934). 

 These data follow the determinative method suggested by T. V. Barker (1930). Allow- 

 ing a possible error of ± 1° in the measured cr value, fifteen compounds are found to 

 have cr values ranging from 290 to 31^°. Several of these are soluble in water and there- 

 fore are excluded ; of the remainder only the salt commonly known as calcium oxalate 

 trihydrate, CaC204.3H20, possesses the same appearance and optical properties as the 

 crystals under consideration. The cr value tabulated by Donnay and Melon for 

 CaC204.3H20 is 30° 7'. The presence of calcium in the deep-sea crystals was readily 

 confirmed by dissolving one in a drop of dilute sulphuric acid and obtaining gypsum 

 needles. A test for the oxalic acid radicle would, however, have consumed most of the 

 crystals so far separated from the Weddell Sea deposits ; certainly a complete chemical 

 analysis was out of the question.^ 



A less direct method of confirming the above identification was therefore sought. The 

 methods described by A. Souchay and E. Lenssen (1856) for synthesizing CaC204 .3H2O 

 did not promise a product sufliciently pure for chemical work. "Envelope" crystals 

 are also present in the cells of certain plants (A. W. P. Zimmerman, 1892), and in the gall 

 and urine of many mammals and fish. No reference, however, has yet been found to 

 crystals of plant or animal origin measuring more than 0-17 mm. across, so that a 

 separation of the requisite amount for exact chemical analysis would probably be 

 impossible. It was suggested by Mr Hey that larger crystals of the compound might 

 constitute the coating of certain renal calculi. This suggestion proved valuable. At the 

 invitation of the Curator of the Royal College of Surgeons I was permitted to examine 

 all their specimens of renal calculi taken from human bladders. Two calcium oxalate 

 calculi were found coated with platy crystals, and these were kindly loaned to the 

 Mineral Department for investigation. 



The calculi differ somewhat in appearance ; one, catalogue number C. 90, is spherical 

 in shape, diameter 25 mm., and has a white powdery surface encrusted with white 

 translucent platy crystals with clear edges. The second calculus (an unregistered dupli- 

 cate) is roughly ellipsoidal in shape, measures 25 x 15 mm., and is encrusted with pale 

 brown crystals of the same type. The matrix like that of C. 90 is white but more com- 

 pact. Golding Bird (1842) has described similar renal calculi from the Guy's Hospital 



1 Unpublished. - The crystals weigh approximately i x lo"^ gm. each. 



