Mr. W. Herapath on Opahe Crystallized Carbon. 423 



of the new ones to detail more fulh' their phms, that it may be 

 seen whether they are Hkely to possess advantages sufficient 

 to overcome the considerations of bulk and price, and to in- 

 duce persons of science to sanction the undertaking. 



I remain, &c. 

 Lewes, May 18, 1823. J, W. Woollgar. 



P.S. In reply to the inquiries of Mr. Innes, in your last 

 Number, I have to observe that the third portion of the Zo- 

 diacal Catalogue is nearly completed, and I trust will appear 

 in your Number for June. I never intended to abandon the 

 work, although circumstances have occasioned a temporary 

 suspension. 



LXXXVI. On Opalce Crystallized Carbon. By William 

 Herapath, Esq. 



To the Editors of the Philosophical Magazine and Journal. 

 TN January last, while performing some experiments on the 

 -*■ relative lighting powers of oil and coal gas, my attention 

 was arrested by a singular deposit in the interior of coal gas 

 retorts. I then imagined it to be sulphuret of iron, but the 

 analysis neither gave me sulphur nor iron; in fact, nothing but 

 carbon. The Annals of Philosophy for April last contained 

 a paper on this substance by the Rev. J.J. Conybeare, in which 

 it was stated to be plinnbago. From the scientific attainments 

 and well-known accuracy of that gentleman, I was convinced 

 that some mistake had occurred ; and in a private connnunica- 

 tion I have learnt from him, that accident.illy he had operated 

 upon a part of the mass so near to the surface of the retort as 

 to have been contaminated with a portion of iron; that he had 

 at my suggestion examined on a small scale, with chlorate of 

 potass, a portion more distant from that point, without being 

 able to detect any trace of metallic or other admixture. 



In every gas manufactory this deposit occurs, though it dif- 

 fers in appearance according to the manner of working. In 

 Bristol it is hard and very solid, having a specific gravity of 

 1*865 with a mammillated surface, which, in places, vegetates so 

 as to resemble cypress tress : from some of the spherical faces 

 it is possible to detach thin scales; when broken, its crystal- 

 line form is very visil)le, and may be compared to that of 

 starch. Although it docs not possess a regular cleavage, I think 

 the primitive foini is tlie tetrahedron. When powdered fine, 

 it loses its gray kistrc and becomes u deep black. 



It is very refractory: with the peroxide of copper it requires 

 so much heat that the black glass tubes generally give way 



before 



