228 DR. ORD. 



did assume the form of the dumb-bell and of allied calculi ; 

 and, further, a comparison of the bodies now obtained with 

 figures given by Dr. Beale and others left no doubt that many, 

 at least, of the dumb-bells found in urine by different 

 observers were composed of oxalate of lime. 



But more than this was to be learnt. The meaning of the 

 great variety of the crystals, the conditions determining the 

 formation of each, and the relations held by them each to 

 each, must be sought for. 



To begin, similar experiments were instituted with solu- 

 tions of calcic chloride and sodic bicarbonate, with a view of 

 reproducing the beautiful spheres originally figured by Mr. 

 Rainey. It was here noticed that when the sodic carbonate 

 was in considerable excess only a few spheres were formed in 

 the neighbourhood of the calcium solution, the middle of the 

 plug being filled with large ovoid rhombohedra closely re- 

 senibling the bodies in PI. XV, fig. 4. The suspicion then 

 arose that some alkaline carbonate might have been present 

 in the oxalic solution in the first experiments, and that calcic 

 carbonate might hare been formed and modified the results. 

 The remarkable facility with which this salt was known to be 

 brought into spherical form by colloids made it possible that 

 the form of the oxalate might have been affected by the 

 presence of the carbonate. The solution of oxalate of potas- 

 sium had, in fact, been rendered alkaline by a little liquor 

 potassse, and here was a very probable source of error. 



A new series of experiments was accordingly instituted. 



1. Acetic acid was added in considerable excess to the 

 solution of oxalate of potash and all the carbonic acid ex- 

 pelled. The solutions being now used as before, the plug 

 was found at the end of five days white and opaque Avith 

 deposit in its lower fourth, adjoining the calcium solution. 

 Above this it was almost clear, the acetic acid having, 

 apparently in virtue of its greater diffusibility, driven back, 

 as it were — outstripped (?) — the calcium salt. The deposit 

 corresponded in the main to the oxalic end of the first plug 

 (PI. XVI, fig. 1). At the calcic end were " wheatsheaves'^ and 

 tlie crystalline kind of dumb-bell, mixed with long, narrow- 

 pointed, and very regular tablets ; the octohedra were few 

 and small. In the clear part of the plug were smaller oval 

 tablets, and small, beautifully rounded, thick-waisted dumb- 

 bells of nearly transparent siibstance enclosing a dumb-bell- 

 shaped cavity. These forms dwindled down at the oxalic 

 end to tiny granules, still resolved by the one-eighth-inch 

 objective into dumb-bells, and then found surrounded with 



