the rounded shape of the nodules and their slippery surface rendered it most troublesome to hold them firmly during the sawing operation; moreover, the thin slices thus obtained were so brittle as to be easily broken by the accumulation of sawdust in the bottom of the saw-cut. Another difficulty arose from the presence of minute sparks of black diamond dispersed here and there throughout the mass; whenever the saw struck against one of them the slice was broken. The hand-saw used by the workmen had what is called a "wide-set"; that is, the teeth were bent right and left so as to well relieve it from the pressure of accumulated sawdust; the consequence being that the saw-cut was nearly as wide as the slice of plumbago produced, and hence each pound was reduced to about nine ounces of slices and seven ounces of dust. The result was that the price of the slices, augmented by twenty shillings for the labour of sawing, was brought up in value from about forty shillings to nearly £4 10s. per pound.

On enquiry into this matter, I found that I could purchase the sawdust for about half-a-crown per pound. These facts held out promises of a very profitable manufacture, if I could only succeed either in making a sawing-machine that would be less wasteful of the material, or in finding some means of consolidating this large quantity of dust, without such an admixture of extraneous matter as would prevent its being used in the manufacture of the best pencils.

I first tried the sawing-machine, which I constructed with great care. The principal features of novelty in this machine related to the saws; these were made from the main-springs of watches which had been broken while in use; they were extremely thin, and of a beautifully fine quality of steel. The "set" on the tooth was made especially small, and consequently the saw-cut was so narrow as to waste only a very little of the material in the form of dust. I entirely avoided the clogging of the saw in these narrow cuts, and the consequent splitting-off of the slice, by putting the teeth of the saw uppermost, and bringing the piece of blacklead to be cut downward upon it by the slow motion of a fine screw. By this means the dust fell freely downwards out of the saw-cut, and never clogged the saw or broke a slice of the material.

I was also successful in getting over the difficulty caused by striking against the little black diamond sparks, by the use of a spring friction clutch on the connecting-rod which reciprocated the saw-frame. This delicately-adjusted clutch was tightened up just sufficiently to overcome the usual resistance to the saw; but whenever that resistance was increased by contact with a diamond spark, the friction clutch simply yielded and the saw was rendered motionless, although the machine continued to work until it was thrown out of gear. It was in this way almost impossible to break a slice in the process of cutting; whenever the machine was thus rendered inactive, the diamond was searched for and removed in the usual way, when the sawing process was resumed.

Having thus succeeded in making a machine capable of saving a large quantity of the plumbago which had hitherto been wasted as dust in the ordinary process of sawing by hand, I considered it advisable to bring my invention under the notice of the eminent pencil-makers, Messrs. Mordan and Co., offering to saw their plumbago at a mere nominal cost, and share with them the value of the material saved. Every offer was rejected by them, under the plea that the firm could not suffer their "prepared plumbago" to leave their premises; they, in fact, wished me to put up my machine and work it in their manufactory; but this I declined to do, and consequently I laid the machine aside for the moment in deep disgust at this unexpected rebuff.

I then determined to try and utilise the plumbago dust which at that time could be obtained so cheaply, and after several preliminary trials I obtained leave from a city firm to use in private their powerful hydraulic press, a machine capable, if necessary, of exerting a pressure of 400 tons on the plunger of my experimental mould, which was simply a cylindrical mass of iron, having an internal diameter of three inches. This cylinder was half filled with the plumbago sawdust in a pure state, and the short ram or plunger occupied the other half; it projected above the surface as shown in Figs. 7 and 8, where A, Fig. 7, represents a section of the cylinder in which the plunger, B, is fitted, and C shows a recessed plate of iron on which the cylinder rests. The powder to be pressed is shown at D; in this state the apparatus was placed in a furnace and heated to redness, after which it was removed to the hydraulic press, and the plunger