perfectly white; after which it is to be melted into cakes, or formed into candles.

Of late years the sulphuric acid and other chemical agents have been proposed for shortening the process of bleaching wax, but we are inclined to believe that they have not been successfully carried into practice, as the manufacturers, we are informed, adhere to the old process above described. To what extent chlorine has been applied to this purpose, or in what manner we are not informed, but the process employed by Mr. Davidson, of Glasgow, and very recently patented by him, is stated in the specification to be as follows.

The wax or tallow is heated to about the temperature of boiling water in an iron vessel lined with lead, when the oxymuriate of lime, (chloride of lime) or the oxymuriate of magnesia, (chloride of magnesia) is to be added either in solution with water, or in the dry state, and then intimately mixed and well stirred up with a wooden spatula. When these materials have acted upon each other a sufficient length of time to discharge the colour from the wax or tallow, the lime or magnesia is to be removed by adding dilute sulphuric acid, or some other acid possessing a greater affinity for those earths than chlorine. The whole is then to be boiled, until the earth employed is separated.

:

For the bleaching of wax the solution of the chloride is to be in the proportion of from 14 to 28 pounds of the salt to 112 pounds of water and an equal quantity by weight of the solution and of the wax to be employed in the process. The sulphuric acid should be. of the specific gravity 1.8485, and be diluted with from 20 to 30 times its weight of water.

For the bleaching of tallow, a solution of chlorine of less strength than the above will suffice, and the sulphuric acid should be more plentifully diluted: but the proportions necessary will vary both in the wax and the tallow, according to the quantity of colouring matter that may be combined with them.

SELF-ACTING SAFETY VALVES FOR STEAM

SIR,

BOILERS.

[From the Leeds Mercury.]

I AM induced, in order to prevent the accidents occasioned by the bursting of steam boilers, which are of such frequent occurrence, and generally so dreadful in their consequences, to send to you the drawing and description of a self-acting safety valve, of my invention, (or rather application to a new purpose; a similar valve having been used as a clack for a pump upwards of a hundred years ago.) You will readily perceive, from the several advantages it possesses, that wherever its adoption shall take place, it would scarcely be possible for an accident of this nature to arise. The opening in the lower part of the box, which is fixed on the boiler top, or, if inore convenient, on any part of a pipe having a free communi

cation with it, requires to be of such a size as to allow a free discharge of all the steam the boiler is capable of generating. This opening is covered with a spherical valve, (the outer part of which is brass filled with lead,) of such a size, and consequently weight, as to press with as many pounds per square inch, as it is intended the strength of the steam at a maximum in the boiler should ever be raised to; the obvious effect of which will be (owing to its being perfectly free from friction) that, at the very instant the steam arrives at that degree of pressure, the ball will be raised, and a discharge instantly take place (The projections are merely to prevent the hall at any time from falling off its seat.)

From the nature of its construction, requiring no packing or attention, it can be entirely secured from the interference of careless attendants, and a pipe may be attached to the branch of the box, and continued into the chimney, or any other convenient place of discharge. I should not recommend this valve to be used as a substitute for the ordinary safety valve, (improperly so called) but in all cases in addition, and so loaded as only to be brought into action at a very trifling additional pressure above that to which the other valve is weighted. This valve would be found of the greatest advantage, in preventing the boiling over of the feed pipes of boilers, when the rooms over them are used as drying stoves in print-works, bleach-works, &c.

I ought to state that I have had this description of valve in use for upwards of four years, with the greatest regularity of action. In the hope that the cause of humanity will in some degree be benefitted by this communication, Steam-Engine Manufactory,

Belton, Lancashire.

I remain, Sir, your's,
BENJAMIN HICKS.

MAYHEW & WHITE'S PATENT SILK-COVERED HATS: THE patentees (Mr. William White, of Cheapside, and Mr. William Mayhew, of Union Street, Southwark,) propose to obviate the two principal objections to silk-covered hats, consisting in their inflexible rigidity, which frequently hurts the head of the wearer, and

in the premature wearing away of the nap at the edge of the crown; by first making the body of wool as usual, then coating the under side of the brim with beaver, and the edge of the crown with stop wool, so as to render the whole as soft and pliable as an ordinary beaver hat. This done, the hat is to be dyed black, or of the proper colour, then stiffened and blocked by the ordinary process, and

afterwards covered with silk.

The fabric usually employed for covering hats is a plush, in which the nap is silk, interwoven in a cotton foundation, the latter being used, we suppose, merely for economy, as our dyers have not yet succeeded in fixing so good a black upon cotton as upon silk. Το prevent the brown appearance of the cotton foundation, when the nap becomes worn off in any part, the patentees propose the simple remedy of making the whole covering, foundation as well as nap, entirely of silk. This improvement appears to us to be supplying a real desideratum in silk-hat making, and one calculated to effect a great economy to the wearer.

PERHAPS the following remarks on the Area of Circles may not be unworthy the notice of some of your numerous readers. The area of a circle, of one-eighth of an inch in diameter, is about 012271846303085.

The area of a circle, of one inch in diameter,

being 78539816339744 decimal of an inch,

divide it by 144, or
what is the same, by 12) 065449846949786

and by 12) 005454153912482 will be the decimal of a foot. This call A, and proceed as above for the area of a circle of one foot in diameter, and others increasing by one inch each. By these notations it may be observed that the primitive circle is preserved in the formation of every succeeding circle, and does away the necessity of coining names for the fluent and constant increasing quantities.

I am your most obedient Servant,

London Mechanics' Enstitution.

On Wednesday, the 24th instant, Professor Millington concluded a course of nine Lectures on the Philosophy and Application of Mathematics. In this course the professor introduced and explained to his auditory a variety of subjects of great importance to all classes of society; and the members of the Institution evinced, by their crowded attendances, that they felt the importance of the Lecturer's choice of subjects, and, by their approbation at the conclusion of the various demonstrations, that they fully understood and appreciated his reasoning.

After the Lecture the chairman announced that Mr. Cooper would commence a course of Chemical Lectures on Wednesday, the 31st instant, which would be continued each succeeding Wednesday; and that Mr. Hemming would deliver his Second Lecture on the Chemical Properties of the Atmosphere, on Friday next.

History of the Steam Engine, Chap. V.
Continued from p. 336.

"When very high temperatures are not to be employed, the kind of boiler just described is found to answer very well; but where the utmost force of the fire is desirable, Mr. Woolf, for a reason which shall be afterwards mentioned, combines the parts in a manner somewhat different, though the same in principle.

"In Fig. 2, A is the main cylinder crossing the smaller cylinders a a a, half way between their middles and ends, but not joined to any of them excepting the middle one at the points at which it crosses them. It is put in this place that it may come over that part of the furnace, SSS, Fig. 1, through which the flame first passes, and receives its direct action, which it does over nearly a half of its surface, as may be seen by looking at the vertical section, ASS, Fig. 1. The smaller cylinders have a communication with the main cylinder in the following manner :-Three cylinders, CCC, are placed parallel to