PURIFYING QUICKSILVER. DIFFERENT EFFECTS OF FROST Sir,-In your valuable Magazine, No. 168, page 205, a correspondent desires to know, why the surface of a square of glass fitted to a frame of wood should be frozen, while one fitted to a frame of iron remains perfectly clear. The explanation given by " Alpha Beta," in a succeeding Number, page 238, may be correct, though I should suppose that glass is little inferior to iron as a conductor of caloric; be this as it may, I have certainly, in considering the subject, been brought to what appears to me a more plausible conclusion. I have observed squares of glass fixed in frames of lead, and secured by large iron bars, which have been frozen over equally with those adapted to wooden frames. But let a current of air be admitted through an aperture, and that part of the glass near to the aperture will remain clear; or should one of the squares be cracked, so as to admit a very slight portion of air, it will be observed that the glass on each side of the fracture will be clear also. 335 PURIFYING QUICKSILVER. Sir, In anwer to your correspondents inquiry (p. 300, vol. vii.) respecting “the bestmethod of freeing quicksilver from its impurities," I beg to inform him that distillation in an earthen retort, is the best and most certain process; and next to that, nitric acid, poured upon the metal, sufficient to cover it, in a broad unglazed earthen vessel, (glass is preferable). Stir with a glass rod, or pipe-shanks; a crust will be formed in two hours, which remove, and pour the purified quicksilver into a clean, dry glass vessel, through a funnel made of writing paper, the edges of which, must be cut with a sharp instrument and not torn; the end of the funnel must terminate in a minute opening, the finer the better. Should the requisite degree of purity be not attained, the operation must be repeated until the metal pass through the funnel without adhering to the paper; it will then be found sufficiently pure for barometrical and thermometrical purposes. I have adopted this method for years and never failed. A small portion of the quicksilver is necessarily lost by the action of the acid, but not of any consequence. N. B. avoid the fumes which arise. I am, Sir, &c. T. W. WANSBROUGH. May we not account for the different effects produced, thus?-That in the instance adduced, the bars of iron were so connected with the glass, that the vapour might attach Fulham, May 16th, 1827. itself to the iron in preference to the glass, as is the supposition of " Alpha Beta," though the contrary was the result, the glass being frozen over. That by the action of cold upon iron it abstracts, while wood remains the same; that when the former contracts, it must produce an aperture, through which a very inconsiderable portion of air may be admitted; it has been already shown that where a current of air is found, there the glass remains clear. An aperture having been effected by the contraction of the iron frame, the inference we make is, that the square fixed in that frame remains perfectly clear and dry. CALLET'S TABLES BY BABBAGE. I am, Sir, your's, respectfully, QUESITOR. Sir, I deem it of some importance to inform your mathematical correspondents, that there is an inexcusable defect in printing the sheet marked r, of Babbage's copy of Callet's Table of the Logarithms of Sines and Tangents. It is true, all the pages of the necessary Loga rithms are contained in that sheet, but the book-binder must cut a part of the sheet at the back margin, which is very awkward, before he can place the leaves of the columns in proper sequence, a circumstance which it is not likely the binder would observe, unless he is previously made aware of it. With regard to the paper of this work, not to mention its peculiar 1 336 CURE OF THE AGUE. colour, the Editor has copied his eminent prototype, in having it printed on that which is palpably too thin. How much more would it have been to his credit, to have made use of a thicker paper, and have made a proportionable extra charge? Let any candid person compare the paper of Gardiner's Logarithms, quarto edition, with the paper of this new performance, and the inferiority of the choice will be too apparent. I remain, Sir, your obedient Servant, W. PITHOUse. May 15, 1827. CURE OF THE AGUE. Sir, I have just seen the reply, (or rather what might be termed the no reply) of Mr. Mellish to the enquiries of W. A. on the care of what are, in our country, generally called Agues. The sum and substance of Mr. Mellish's letter appears to be, that quinine taken three times a day is a specific remedy for the ague, leaving the dose and manner of taking it to W. A.'s. conjecture, which defect I shall endeavour to supply to the best of my judgment. ac I would recommend to W. A. or any other grown up person, to take · the quinine in doses of a grain and a half each; it would be better to go to some respectable druggist who can be depended on (for there is no article so much adulterated,) and purchase a few doses of it alone, and then, that he may more curately divide so small a quantity, I would have him add to it a small quantity of powdered loaf-sugar, which having well mixed with the quinine, he may divide into as many papers as there are doses, one of which let him take in wine and water every two hours. Should he, while taking the quinine, experience a return of the paroxysms, he must immediately give over, and not re-commence until the paroxysm has subsided; this mode of treatment, if persevered in, I have little doubt will always prove successful. In no disease is it more important to attend to habit of body; I should Corrigenda et Addenda. In Mr. Davy's Account of the BellCrank Steam Engine, in last number, the at two feet, instead of sixteen inches. The stroke of the piston should have been stated following are some additional dimensions:-Crank stroke, 1 foot; diameter of the air pump, 10 inches; diameter of the piston rod, 24 inches. NOTICES TO CORRESPONDENTS. A reply from "Aurum" to "Platinum," on the Attendance of Females at Anatomical Lectures, with corroborative letters from T. M. B.; H. Massingham; L. L.; and "One of the Sex;" were all received at too late a period of the week for more particular notice in this Number. Other acknowledgments are, for want of room, deferred till our next. Communications (post paid) to be addressed to the Editor, at the Publishers, KNIGHT and LACEY, 56, Paternoster Row, London. Printed by Duckworth & Co. 76, Fleet-st. 338 ON THE PROPORTIONS OF STEAM ENGINES. ON THE PROPORTIONS OF STEAM ENGINES. NO. II. compare the dimensions; and 1 flatter myself that the drawing will be found perfectly accurate; therefore to that I will refer your inquiring readers. Mr. Perkins informs me, that in his engines, he prefers High-Pressure Engine, at Whit- having the piston-rod one-third the bread's Brewery. Dear Sir, In this second example I have introduced an engine as worked by high-pressure steam. Engines of this description have been generally considered unsafe; but as their superior efficiency renders them, in many situations, peculiarly eligible, and the danger which attended them may be considered as entirely removed by the scientifie improvements of Mr. Perkins and others, I have no doubt that they will shortly be in as common use as the low-pressure engines have hitherto been. An engine precisely of the form represented in the prefixed engraving is used at Messrs. Whitbread's brewery, for supplying water to the large steam boilers employed for boiling the liquor (by steam). Being used, however, only to the extent of one horse power, the parts are so small, that the drawing is enlarged sufficiently for an engine of seven horse power, similar to one erected by Messrs. Taylor and Martineau. Description. Near A is a dotted circle, intended to shew the situation of the steam pipe conveying the same into the cylinder. B shews the handle of the cock, which alternately admits the steam above and below the piston. Its action will be seen by supposing, that when the slide and rod C, which is attached to a cross bar working the vertical slide rod H, is carried upwards, it strikes against the handle B, and produces the alternating motion required. A small pipe and valve is placed under the cylinder, to relieve it of the condensation which will always take place. This being a pumping engine, the eccentric E will fully explain how this motion is effected. I have attached a scale by which to diameter of the piston; but no specific rule can be laid down, as I have seen engines of six horse power, &c. &c. employ a piston-rod as large as that used for twenty. Mr. P. considers his proportion would be double, but an advantage to a a disadvantage to a In his (Mr. single-acting engine. 66 P.'s) connecting rods, he considers two and a half for the length of the stroke to be the proper proportion. But he also observed, that where there is room, (in a factory, for instance) he would employ one of four times the length of the stroke. While on the subject of proportions, it would be gross neglect if I did not introduce a plan shewn by Mr. Kirby, in one of his late excellent lectures on the steam engine, at the London Mechanics' Institute-a plan which I believe has never been published, shewing the method of obtaining the length of the radial dium of Mechanics," has given a rod. Brunton, in his Compenmethod; but as he has placed the links of the parallel motion equidistant from the fulcrum of the beam, the radial rod of course becomes of the same length as the parallel bars. It however happens in many instances, that the air pump is nearer the end of the beam towards the cylinder; and when that is the case, the radial rod becomes longer. The following is the operation, (see figs. 2 and 3, in which, to make the matter clearer, I have shewn the beam, &c. &c.) In designing an engine with a beam, (which you must commence with) let one-half the length be represented by a ba the fulcrum, fig. 3; describe the arc bbb, such being the length of the stroke; draw the base line bd, fig. 2, and in the centre of the • We wish our other correspondents would in all cases adopt the same plan. It would add greatly to the practical value of their communications.-EDIT. 3 arc draw the horizontal line b a. Take half the versed sine, or pitch of the arc, and draw a perpendicular line, shewn at c; this will be the centre of the piston-rod. Now determine the length of the link b e, (which is often made the same size as the crank), and from the point b at the top, to wherever it touches the centre line of the piston, it will shew the real inclination of the link towards the piston-rod. Now, sup ON THE SECTOR, BY MONAD. (Continued from page 312.) THE LINE OF TANGENTS. For the line of tangents, at D (see elementary figure, page 189, vol. vii) erect the perpendicular D G unlimited towards G; draw strait lines from C, through_the several divisions of the arch A D, to meet the straight line D G; the points of concourse mark the divisions of a line of tangents. Transfer the several lines, thus intercepted between C and D G, to the line A F, beginning from A; A F is now a line of secants. The line of tangents is distributed upon the sector pose at g we have the other link, ee will have to be drawn parallel to the centre line of the beam, which will be the parallel bar; continue the line through (dotted), and make an Isosceles triangle of the same area or size as the one marked, only observing to let the base line of this triangle be formed by the line c of the piston, as shewn at 1, 2, 3. Draw the centre line of this triangle ƒ ƒ 3, and make ƒ ƒ equal to e e, and lastly, obtain a centre (the method shewn by the radius I), to describe the arc e ƒ H, which will be at K; therefore Ke will be the length of the radial rod. I remain, Sir, Your's respectfully, CHRISTOPHER DAVY, Teacher of Architecture, Perspective, &c. L.M. I. and 11, Furnival's Inn. in two lines, the outermost of which, extending to 45°, has the same radius with the other double lines. The inner line of tangents extends to 75°, and is calculated to a less radius; generally, I believe, one third of the former. The line of secants extends also to about 75°. The hour line used in dialling, is a line of tangents to 45°, and is thus to be drawn:-Divide the semiquadrant a B into three equal parts; through each of these points draw lines from the centre C, to meet the tangent B N. Transfer these divisions to the tangent B M on the other side B; then M N is the hour line. The quarter points are ob |