THE TECHNOLOGIST. [May 1, 1864. 



470 THE PATENT PLUMBAGO CRUCIBLE COMPANY. 



and sent from the Eattersea Works in the form of ordinary " black- 

 lead." As this article is used wherever there is a grate or stove to be 

 kept bright, its annual consumption must be very large. There is no 

 substitute for it — nothing that can be employed in the same way to 

 polish and protect the ironwork of common fire-places. Without the 

 factitious lustre produced by the action of " elbow-grease" on black- 

 lead, the most elaborate kitchen range would soon become unsightly, 

 the trim parlour grate would blush with rust, and the cottager's " wee 

 bit ingle " would leave off " blinkin' bonnily." 



The various qualities of black lead which the Company sends into 

 the market under different fanciful names are all prepared from graphite 

 or plumbago, and nothing else. The higher qualities are distinguished 

 from the lower by their superior fineness, softness, and lustre ; but 

 chemic illy they are identical. The article sold under the sentimental 

 name of " Servants' Friend " at 28s. per cwt. is quite as pure as the 

 " Prize Medal Lustre," which fetches double the price, or " Halse's Ro- 

 man Lustre," the best quality of black lead manufactured by the Com- 

 pany. Again, the analytical chemist would fail to detect any essential 

 difference between either of the above-named products and the article 

 labelled " carburet of iron," in remembrance of the exploded opinion 

 respecting the nature of graphite. How comes it, then, that one quality 

 is so much superior to another? The explanation is simple enough. 

 The differences in the manufactured article may be traced to certain 

 variations in the physical properties of the raw material. Thus one 

 sample of graphite may be soft and lustrous, while another, equally 

 pure, may be hard and dull. These variations are subordinate to the 

 distinction between amorphous and crystallized graphite, to which we 

 have already referred. For making domestic black lead, the amorphous 

 or soft graphite is almost exclusively used. 



The separation of the different qualities of graphite is a labour which 

 demands great experience and judgment, and can only be successfully 

 performed by the old hands. The best pieces are soft and unctious, per- 

 fectly free from grit, and capable of receiving a very high polish. The 

 worst pieces, technically called " gruffs," are, on the contrary, harsh, 

 gritty, and deficient in lustre. The latter are only employed for making 

 " leads" of the lowest brands. The numerous intermediate qualities are 

 distinguished one from another by characters which are only apparent 

 to the experienced eye. 



The manufacture of black leads includes three distinct operations — 

 grinding, sifting, and packing. At the Battersea Works, the first opera- 

 tion is performed by means of a large mill driven by steam power. The 

 ground "lead" is conveyed to an upper floor by an endless-band 

 elevator, and is then sifted through the finest silk in the simple dressing 

 machine already noticed. The packing is chiefly done by boys, who 

 work with marvellous rapidity. The powdered black leads are done up 

 in neat packets in quantities from two ounces upwards ; they are also 



