45 
( CaOH 
be found to agree with the formula 0 | + 7 H 2 O, which 
loses on heating 49179 per cent. The number found by 
Rose (49 '084) agrees very nearly. 
The salt is perfectly stable for any length of time if kept 
out of contact with the air. It may be also kept unaltered 
in the mother liquor for some time. In the air it decom- 
poses, absorbing carbonic acid and water. Over sulphuric 
acid in vacuo or in air, or over quicklime, it parts with a 
portion of its water of crystallization. Both these circum- 
stances interfere with the exact drying of the salt. 
With water, it decomposes into calcium hydrate and 
calcium chloride — 
2 [ 0 1 ] + 2 H 2 O = 3Ca(OH)2 + CaClj . 
By the substitution of hydrobromic for the hydrochloric 
acid in the preparation of the salt, I expect to obtain a cor- 
responding bromine compound. 
'‘On the Structure of Stigmaria,” by Professor W. C. 
Williamson, F.R.S. 
At the meeting of the Manchester Literary and Philo- 
sophical Society, held on October 20th, Mr. Binney called in 
question some conclusions at which I had arrived, and had 
published in Part II. of my Memoirs on the Structure of 
the Coal Plants, respecting the organisation of Stigmaria. 
Mr. Binney further published an abstract of his remarks in 
Part II. of Vol. 14 of the Society’s Proceedings. Believing 
that Mr. Binney’s observations, if allowed to pass unnoticed, 
may mislead some Palseontologists unacquainted with Stig- 
maria, I feel called upon to reply to them through the same 
channel as that which he has employed for their promulga- 
tion. The general features of the plant, known for half a 
century as Stigmaria ficoides, have been so well described 
by Bindley and Hutton, Dr. Plooker, Miv Binney, and Brong- 
uiart, that no one familiar with those descriptions can fail 
to recognise io without difficulty. That plant consisted of a 
