To practical chemists the mere announce

ment of a new and enlarged edition of this val- THE monthly report of Mr. William Crookes,

uable work is sufficient. The first edition was exhausted some time ago.

The new methods introduced into laboratory practice since the first edition was written, have rendered a thorough revision necessary. Much of it has been rewritten, and an amount of new matter added nearly equal in volume to the original work.

It is now a book of 725 pages. The processes that are commonly known are purposely omitted, the main object of the author having

Dr. William Odling, and Dr. C. Meymott Tidy shows that the character of the water supplied to the metropolis (London) during the past month has been in every respect excellent. The mean ratio of brown to blue tint of color in the Thames-derived water was found to be as 11.4:20; while the mean proportion of organic carbon was .128 part in 100,000 parts of the water, with a maximum in any one sample examined of .148 part; this maximum of organic carbon corresponding to just over a quarter of a grain of organic matter per gallon.

ELLHOFFITE.-Comparative trials have been

been to bring into notice a number of little-H made at St. Petersburg respecting the

known expedients and precautions which prevent mistakes, insure accuracy, and economize time.

TREATISE ON BELTS AND PULLEYS. By J. A HOWARD CROMWELL, Ph. B. New York:

explosive effects of ordinary gunpowder, nitroglycerine, and a new explosive known as hellinvented by Hellhoff and Gruson, is a solution hoffite. The latter, which has been recently of a nitrated organic combination (naphthalene, John Wiley & Sons. No mechanical engineer will dispute the de- phenol, benzine, etc.) in fuming nitric acid. In sirableness of a reliable treatise on Belting.ments, binitrobenzene, a solid, inexplosive, and preparing the hellhoffite tried in the experiThe discordant results obtained by the differ-badly burning substance, was used. At the ent rules given by leading authorities are exceedingly confusing.

The work before us shows evidence of careful preparation, and of complete knowledge of the subject.

The large number of examples will prove to be a valuable aid to the young engineer.

A

PRACTICAL TREATISE ON HYDRAULIC MINING IN CALIFORNIA. By AUG. J. BOWIE. New York: D. Van Nostrand.

An estimate of the scope of this work can be well made from the list of topics treated by chapters. They are, in order, as follows:

first trial, glass bottles of 20 cubic centimeters contents each were filled with 25 grammes of the respective explosive substances and corked down. A tube filled with fulminate of mercury being attached to the outer end of the tube for was passed through the corks, a slow-match the purpose of ignition. Each of the bottles thus prepared was placed on a truncated cone of lead, the upper diameter of which was 3.5, its lower 4.5, and its height 6 centimeters. The cone itself stood on a cast-iron plate 2.5 centimeters thick. The deformation of the leaden cone by the action of the explosives could conChapter I.-The Records of Gold-Washing. sequently be taken as a measure of their respectII.-History and Development of Placer-Min- ive destructive power. The explosion of the ing in California. III.-General Topography gunpowder, as was anticipated, caused no and Geology of California. IV.-Distribution change. By the explosion of the nitro-glycerof Gold in Deposits, and Value of Different ine, the cone was compressed about a quarter Strata. V.-Amount of Workable Gravel Re- of its height; its surface had assumed the apmaining in California. VI.-Different Meth-pearance of a well-worn hammer; the diameter ods of Mining Gold Placers. VII.-Prelimia- of the surface had been increased to 5.5 centiary Investigations. VIII.-Reservoirs and meters. The explosion of the hellhoffite caused Dams. IX.-Measurement of Flowing Water. much greater changes. The surface of the cone X.-Ditches and Flumes. XI.-Pipes and was completely torn; pieces 5 centimeters long Nozzles. XII. Various Mechanical Appli- and 2 centimeters thick were torn off, and XIII.-Blasting Gravel Banks. XIV. thrown about for several paces; only half of -Tunnels and Sluices. XV.-Tailings and the cone was still a compact but entirely deDump. XVI.-Washing, or Hydraulicking. faced mass. At the second experiment, bottles XVII.-Distribution of Gold in Sluices. XVIII. (of 25 grammes each) filled with the various -Loss of Gold and Quicksilver. XIX.-Duty explosive substances were let into correspondof the Miner's Inch. XX-Statistics of Cost ing cavities bored into the face of fir blocks of of Working and Yield of Gravel. similar dimensions. In exploding the gunpowder, the block was torn into four pieces, as if split with a hatchet; the several pieces were thrown about for 18, 12, 11, and 10 paces. In exploding the nitro-glycerine, the block was split into several pieces. The upper portion of the block, as far as the bottle was let into it, was torn off perpendicularly in the direction of the fiber in such a manner that a smooth cut was formed. The explosion of the hellhoffite likewise tore the portion of the block surrounding the bottle perpendicularly in the direction of the fiber, and splintered the remainder of the block into a large number of thin fibers. The following experiments were also made with hellhoffite alone. A slow-match was passed

ances.

The printing and illustrations, including maps, are excellent.

THE

MISCELLANEOUS.

HE Russian papers say, that, at the request of General Komaroff, Governor of the Transcaspian region, the Minister of War has recognized the urgency of immediately establishing a line of telegraph connecting Merv with Askabad. This line would pass by Annow, Babadoorma, Bougatchik, Artchigan, and Sarakhs. Its length will be 500 versts, and the expense about 100,000 roubles.

A

through the tube in the cork without fulminate survive in ordinary use at Portsmouth, Devonof mercury as far as the surface of the hellhoff-port, and Sheerness. These were built of seaite in the glass bottle; no explosion followed soned timber before the age of hurry set in. on igniting the slow-match. A quantity of MECHANICAL AIR PURIFIER.-An apparahellhoffite poured into a bowl could not be extus for purifying air from dust, germs, ploded by a lighted match. Finally, a few or other impurities, has recently been designed drops of hellhoflite were poured on an anvil, by M. Windhausen. It consists of two horiand exposed to heavy blows with a hammer, zontal concentric cylinders placed in connection and no explosion followed. The hellhoffite, with a fan. The fan and cylinders are fixed consequently, possesses the following advan- upon and turn with the same shaft, and the tages: (1) In igniting it with fulminate of mer- whole is enclosed in a casing. The cylinders cury, it acts more powerfully than nitro-glycer- are closed at the ends with the exception of a ine. (2) It may be stored and transported with hole permitting the passage of the air drawn in perfect safety as regards concussion, as it can- by the fan. As the air passes through the connot be exploded either by a blow or a shock, centric space between the drums, it is caused nor by an open flame. On the other hand, it to rotate with them by means of feathers runhas the following disadvantages: (1) Hellhoff-ning longitudinally on the inside of the outer ite is a liquid. (2) The fuming nitric acid con- cylinder. The shaft which carries the whole tained in hellhoffite is of such a volatile nature arrangement is hollow, and serves to convey that it can be stored only in perfectly closed water which is allowed to escape therefrom invessels. (3) Hellhoffite is rendered complete-side the drums by means of small holes, which ly inexplosive by being mixed with water, and can consequently not be employed for works under water. It would, therefore, be injuriously affected by exposure to damp, and, moreover, there are no records of its behavior under extremes of temperature. Without some experiments in this direction, in our opinion, all the rest is comparatively valueless.

Ε

FFECT OF ENCASING WOOD WITH IRON.

It was always expected, since first wooden ships were clothed with armor plates, that they would speedily decay, and this anticipation has been abundantly realized. The only excuse

project it in the form of fine spray against the inside of the inner cylinder. This cylinder is also perforated, and the water again escapes from it and is projected against the inside of the outer cylinder, over which it spreads as a thin coating. The motions of the air and water are as nearly as possible in opposite directions. The water, after it has been sufficiently exposed to the air, is allowed to escape, and is drawn off by means of a siphon. The same arrangement may be modified for treating smoke or

gases.

ELEGRAPHS IN CHINA.-We learn from Na

for the armor-plating of the Lord Clyde, Lord Ture that telegraphs are extending with Warden, Ocean, Prince Consort, Caledonia, extraordinary rapidity over Southern China. Zealous, Royal Oak, Repulse, Royal Sovereign, At the present moment, Pekin, in the far north, Favorite and Research, was the fact that the is connected by a direct line through Canton vessels were already built or building, and with Lungchow, on the frontier of Tonquin, were of no use at all unless so protected. When the extension from Canton to the latter place once those ships of the line were completed having been made during the recent war purethat happened to be on the stocks when ironly for military purposes. We have thus one clads were proved to be an absolute necessity, no other wooden ironclads were laid down in great line stretching through the Chinese Emthis country, but iron ships took their place. pire from north to south, and at the present But in France wooden ironclads continued to moment an important line is being constructed be built until within the last eight years, and it along the southern borders of China, through is this fact which has doubtless induced the Yunnan. Starting from Nanking, in Kwansi, the provinces of Kwantung, Kwangsi, and French Admiralty to lay down so many iron where it joins the Canton-Lungchow line, it and steel ironclads since that time. It is the will extend for nearly 600 miles to Nung-lik, in closely-fitted wooden bicking on the outside and South Yunnan, running for half the distance flanking on the inside which entirely prevents air from getting at the unseasoned oak timber of along the Yukiang, the name of the Canton River in its upper course. The work is being the frames, and this causes the juices of the carried out by the Chinese themselves, with the timber to ferment, and so induces the growth assistance of one European, and it is stated of the peculiar fungus known as dry-rot, An that during the recent war the Canton authoriexamination of our wooden ironclad fleet a few ties equipped a complete field telegraph staff, years ago resulted in their being almost en- the members of which were so thoroughly tirely condemned, and now we find the admir- trained that they have been able to put up 35 alty are turning them into money by sell- miles of line in a single day for war purposes. ing them to the ship breakers. The Royal

Sovereign-the ship in which Captain Coles' Telegraphs have now secured a firm footing in turrets were first tested-also the Zalcus and China, and their extension over the whole Favorite, have just been sold for this purpose, country is a matter of time only. and others will doubtless speedily follow.

While vessels of less than twenty-five years old

are thus being broken up on account of rottenness, it is interesting to notice the number of two and three-decked wooden ships-some of them nearly a hundred years, and none of them less than thirty or forty years old-which still

THE Organe des Mines seriously states that a

company is about to establish large works for making rails from paper near St. Petersburg. The paper is subjected to great pressure, and it is said that the material is extremely durable and can be produced at one-third the cost of steel rails.

VAN NOSTRAND'S

ENGINEERING MAGAZINE.

NO. CCVII-MARCH, 1886.-VOL. XXXIV. :

THE FLOW OF WATER OVER SUBMERGED WEIRS.

I.

BY EDWARD SAWYER.

Written for VAN NOSTRAND'S ENGINEERING MAGAZINE.

Under the title "The Flow Through Submerged Outlets," there appeared in the June number of this Magazine, a translation of an article by M. Alfred Salles, published in the "Memoires of the Bureau des Ponts et Chausées" for 1884, -which will grievously mislead those who take it as embodying the present state of knowledge on this subject.

The writer attributes to M. Mary, under date of 1860, the following formula, for the delivery through partly submerged sluices,

Q=mLH'√2gx (H−H'+h) in which L is the length of the sluice, H is the height of the water on the up

stream side above the sill of the sluice, H' is the height of the surface on the down-stream side above the same level, h is the height due to the velocity of the current on the up-stream side, and m is a coefficient not experimentally determined, but assumed to be about 0.8.

M. Salles then substitutes in this formula, numerical data obtained at a dam across the river Garonne, at Toulouse, and deduces 0.82 as an approximate value for m, "agreeing remarkably with M. Mary's anticipation."

A brief examination will show that this agreement is purely accidental.

height of the backwater,-it takes H' as
that if the channel below the dam were
the depth of the stream. It is obvious
that if the channel below the dam were
deepened so as to lower the backwater,
other data remaining the same, Q would
be increased; but this formula makes it
to the crest of the weir, in this way Q
decrease. Drawing the backwater down
decrease it to nothing.
would increase while the formula would

This absurdity results from confounding the case of flow through a sluice with the radically different one of flow over a weir. For the latter case, the formula in question misrepresents both factors of the discharge-the depth of stream, as the case of free discharge over a weir, it above shown-and also its velocity. In is universally admitted, and indeed is easily proved, that the velocity of discharge, at AB or CD (Fig. 1), increases

Fig. 1

B

D

This formula makes the value of Q de- from the surface downwards. In flow pend directly upon that of H', or the over a submerged weir, the velocity must VOL. XXXIV.-No. 3-13

Dubuat had a good understanding of this subject more than 100 years ago. In his "Principes d'Hydraulique," t. I., §§ 141-147, editions of 1786 and 1816, he elaborates the general theory, dividing the stream into a free section acting like an unobstructed weir with velocity increasing from the surface downwards, and a submerged section acting like a SUBMERGED rectangular orifice of the height H' and under the head

its bottom in the same level plane with the bottom of the channel and aperture (Fig. 3), and his discussion is based upon observations of the conditions of flow through this aperture.

One characteristic of a weir is that it produces bottom contraction; and contractions are suppressed, or else the narrowing of the stream caused by them is rebated directly from the length of the In beginning his examination of the weir. With this apparatus there was no subject, Lesbros refers to Dubuat's bottom contraction, but instead thereof, "Principes, t. I. §§. 141-147, but instead two end contractions, with falls varying of taking the theory there set forth, he from .0027 m. to 135 m. turns to t. II. §. 413, etc., where Dubuat describes the small weir (0.11 m. high there would have been no sudden fall In fact, without these end contractions and 0.47 m. long), with which he made here, only the slopes appropriate to flows four experiments with free discharge, and in a uniform channel. one with the flow obstructed by backwater. For the case of free discharge Dubuat concludes that 9 varies with (H+h). From this, Lesbros appears to have evolved the formula for sub- into a deep channel of escape, had to flow merged weirs,

q=m(H+h)√2g(F+h),

Neither was there any deepening of the channel down-stream from the aperture; hence the water, instead of falling

over the level floor. Thus, the depth down-stream from the aperture affected 7, not merely by limiting the fall, but also as being the depth of a section through which all the water had to pass after leaving the aperture. H' cannot be reduced to 0, because no water can flow in a stream of no depth, though Lesbros exterpolates coefficients out to this impossible extreme.

which he says-falsely so far as I see that Dubuat indicates. Having thus ignored Dubuat's whole theory as stated in §§. 141-147, and set up in his name a a formula utterly inconsistent with it, he undertakes to demolish the latter by saying that if it expresses the true law of the phenomena, it is evidently suitable Probably Lesbros, in trying to simplifor déversoirs formed at the entrances fy the expression, reasoned that all the of canals like those with which he experi- water finally passes under the acceleratmented, i. e., with apertures starting from ing action of the net head F (in reaching a level floor, because the escaping stream the section of minimum depth H'), hence is partly submerged in both cases, where- that this fall should be taken as acting as he finds, by putting the data from his on the whole stream, but apparently he aperture experiments into it, that the was aware that the resistance here was resulting values for the coefficient vary less than that against flow into still wildly, from 4. to 0.287. water, though he left the effect of this and other neglected factors to be covered by the variations in the coefficient. In fact the discharge was made against water moving in the same direction towards an orifice opening into the air. With the water in the reservoir maintained at any given height H, the two components into which it is divided, fall of surface and depth at H', are affected by the more or less resistance to the escape through the channel and orifice. As this resistance diminishes, the depth in the channel diminishes and the velocity there increases. The resulting diminution of resistance to flow at H' allows the velocity there to increase faster than F+h. But the actual velocity of the stream at this place is difficult of determination, in consequence of the varying narrowing of the effective area by the end contractions,

It seems that he reaches this result by a process which Dubuat probably would have condemned, that is, by taking H' at the highest place in the channel below the aperture, sometimes at the lower end, see Fig. 3; for he announces as a result of his study of the subject, that instead of this, it ought to be taken at the lowest place, in the depression at the foot of the fall. Taking it in this way, and neglecting h, which was unimportant in his experiments, he represents the discharge by the expression H √F, with a coefficient varying with the relative values of H and H', but entirely independent of their absolute values, or the scale of the experiment.

But his apparatus was radically different from a weir, and manifestly unfit for showing the laws of flow over one.