308 Royal Society : — - 



The mere fact, however, that the salts are, as a rule, perfectly in- 

 sensible to every kind of surface, wood, paint, paper, glass, and 

 dust of all kinds, seems to me fatal to this theory. 



A solution of one part of normal sodium sulphate in about six of 

 sulphuric acid possesses some curious properties. This solution, 

 which sets quite firm, can be kept for a week in an open beaker, 

 so that the air apparently has no crystals to introduce ; aud yet 

 when dropped on to a dirty surface in my laboratory it more often 

 crystallizes than not. It is thus much more sensitive than an 

 aqueous solution of sodium carbonate or acetate. The crystals are 

 apparently a hydrate of the hyperacid salt NaH 3 (S0 4 ) 2 ; and it is 

 almost inconceivable that the dust should contain crystals of this 

 salt. It is extremely deliquescent, and the excess of acid should 

 certainly be taken up by the dust, and very often by the surface 

 itself. 



The solution sometimes crystallizes suddenly in the test-tube as 

 though something had fallen in. The crystallized drops will not 

 stand exposure to air for more than 30 minutes or so. Hence, 

 although there is plenty of sulphuric acid in my laboratory, where 

 I have often heated this solution, I find it very hard to believe 

 that the salt exists in this form in any part of the room. The 

 normal salt and the anhydrous salt are without action on the solu- 

 tion. It crystallizes in a test-tube in fine stellate masses, with 

 projecting points on all sides, as alum sometimes does ; these ulti- 

 mately coalesce. These crystals are composed of very fine parallel 

 fibres like ferns, and are opaque white. It sometimes sets in long 

 fibres, radiating from different points like aluminium sulphate. 

 Owing to the fineness of the fibres it would be very difficult to free 

 them from the mother-liquor. 



My reason for believing them to be a hydrate is this : — In a 

 beaker this solution gradually deposits clear crystals, varying from 

 very fine needles to rhombic plates, prisms, and short, nearly glo- 

 bular, highly modified forms. These are formed near the top, and 

 may perhaps be different hydrates. They are formed, however, at 

 the same time, and at present I believe them all to be the hyper- 

 acid salt. Similar ones are formed by putting the normal salt 

 in the 6 to 1 solution, and this remains liquid, sometimes dis- 

 solving the crystals. An opaque amorphous mass is formed at the 

 same time, which appears to be hydrated, but it also is inactive. 

 A mixture of two parts of acid to one of salt in a flask, when 

 boiled to get rid of all water, sets firmly in a clear mass, in which 

 the opaque variety makes no chauge. Then if a little water. is 

 added the salt turns opaque white wherever the water reaches ; and 

 this is entirely absorbed, the cake remaining quite dry. 



If this is again melted it deposits clear prisms, leaving a little 

 mother-liquor ; but the opaque variety when introduced from the 6 

 to 1 solution causes the whole mass to set firmly opaque white 

 and become quite dry. The opacity spreads slowly, and a kind 

 of beard of fine crystals can sometimes be seen growing round the 

 prisms at the edge. Lovely foliated films are often formed at the 



