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its contents accurately weighed. The arsenious acid having been removed by hydrochloric acid and water, the empty tube is dried, and again weighed. The difference in weight expresses the amount of arsenious acid in the filtrate, whence the metallic arsenic is calculated. A more critically accurate method would be to dissolve the scrapings in uitromuriatic acid, and to estimate the arsenic acid from the filtered solution by a given weight of metallic iron, as directed for phosphorus.

10. Antimony. The only two substances in cast iron precipitated by the metallic copper are arsenic and antimony, and as the two are frequently associated, and give similar metallic stains, we thought it advisable in estimating one to test for the presence of the other. This was done by adding to the tache on the china a concentrated solution of iodate of potassa, which, according to Slater, (Chem. Gaz., ix. 57,) reddens and immediately dissolves arsenical stains; while upon those of antimony it exerts no visible action for several hours. Chlorinated soda or lime will also instantly dissolve arsenic, and leave the antimony.

11. Sulphur.-If the tache did not indicate an appreciable quantity of arsenic, the preceding manipulations may be omitted; otherwise, after it has been separated, as above directed, chloride of barium is poured into the residual liquor, the whole stirred, and left to repose for several days. If the content of sulphur is very minute, cloudiness does not manifest itself for several hours, and in such cases a week's repose is necessary to insure the entire subsidence. It must then be filtered off, washed with diluted hydrochloric acid and hot water, ignited, weighed, and the amount of sulphur calculated from the weight of sulphate of baryta.

It is proper to observe, in order to provide against the possibility of error, that some caution is necessary as to the nature of the precipitate; for if the solution be concentrated, a portion of the chloride of barium, which is generally added in excess, may ultimately fall in fine crystalline powder, but it will disappear during washing on the filter. The previous acidulation of the liquid prevents the precipitation of carbonate, phosphate, or arseniate of baryta.

NITROGEN, OXYGEN, AND ARIDIUM.

Nitrogen. The doubts of many of the best chemists as to the presence of this element in cast iron, having been confirmed by the recent experiments of a careful investigator, we omitted searching for it.

Oxygen. We doubt the presence of oxygen as an essential ingredient of recently made metal, except in the minute portions of slag accidentally remaining in it, and which sometimes contains a silicate of the oxide of iron.

Aridium.-Aridium, said to have been found in some Swedish ores, was not observed by us in our examination.

August 8, 1852.

ERRATUM.-On page 200, in first column, top line, for “strong acid,” read “weak acid.”

For the Journal of the Franklin Institute.

On Kemp's Gas Thermostat. By CHARLES M. WETHERILL, Ph. D., M. D. Kemp describes in the Chemical Gazette, vol. vi. p. 184, (1850,)* a very convenient apparatus for regulating the heat of a gas burner, which See Journ. Frank. Inst., Vol. xx., Third Series, p. 336.

deserves a cordial welcome by chemists who have lost their time, patience, and frequently their analysis, by the use of the air bath described in the works on analysis. A great drawback probably to the introduction of Kemp's thermostat, is the use of a platinum tube, which he was at last obliged to add, after several inefficient attempts to avoid it. To those who have not seen Kemp's description, it may be necessary to state, that it is an air thermometer, placed in the space to be heated, and so regulated by a tube connected with the gas pipes, that the mercury rising to a certain point in the air thermometer, will close the extremity of the said tube, and thus shut off the supply of gas from its burner, which is fed from a tube leading from the upper part of the air thermometer. The tube slides in a brass stuffing box, and when the temperature has reached the required point, (as shown by a thermometer,) it is pushed down to the level of the mercury, so as to shut off the supply of gas. To avoid the light being extinguished, a small hole is bored in the sliding tube, an inch above its extremity. An inspection of the accompanying figures will make this

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plain. The difficulty Kemp found in employing other tubes than platinum, arose from inefficient contact where no amalgamation ensued, thus suffering the heat to rise "many degrees above the assigned limit;" while copper and brass tubes quickly dissolved in the mercury, rendering it impure, "so that its rise and fall could not be depended upon with the required nicety."

I have found no difficulty in using a glass tube in the place of platinum. Its adaptation depends upon a very simple alteration, namely, of drawing out the extremity. By this means, the extremity of the tube comes in the

centre of the rising column of mercury, which closes it accurately. In order to effect this the more surely, the part drawn out is -inch diameter, and of the same diameter for about 3-inch. A quarter of an inch from its extremity is broken up carefully with a very fine angular file. It will be scarcely possible, with glass tubes, to make this slit sufficiently fine that the light be shut off gradually, as Mr. Westly proposes, (Chemical Gazette, vol. vII. p. 239;) since the area of opening necessary to heat an air bath of ordinary size is very small; but the mercury reaching the glass for a short distance before closing the aperture, enables a very accurate closure. When the column of mercury in this tube is barely sufficient to stop the supply of gas, it lowers the flame somewhat, and by a very rapid opening and closing of part of the hole, gives rise to a humming noise, thus attracting attention to the apparatus. The supply of gas should be so regulated that only a slight excess be allowed for variations of pressure. The intervals of this tone will thus become longer and longer, and the temperature will remain constant. Of course, a too great supply of gas, causing the mercury to rise several lines above the aperture of the sliding tube, will render the equilibrium which takes place between the area of this aperture and the required temperature an unstable one, and liable to be disturbed by any sudden cooling effect. The above mentioned tone, therefore, is not without its use, in calling attention to the apparatus until it be regulated properly.

I have had two of these apparatus in use for some time. One is placed in the oven under my sand bath, (which is a large one heated by gas burners.) When the sand bath is not in operation, the sinking of the mercury in the air thermometer raises the lights in the oven. This thermostat worked well, and gave a constant temperature, both when the sand bath was used and when it was out of action.

The other is adapted to an air bath. This very convenient form of air bath (fig. 1) is described in all the works of Analysis that I have seen as necessary to be brazed. This is not at all important, and adds considerably to its expense; a few rivets will answer the purpose equally well, and the chemist may make it himself. The top, bottom, and sides are of one piece, riveted together, the edges being turned down behind and before, to rivet in the back and for the door. A represents the air thermometer, which is of glass. It is convenient to add sufficient mercury, that when the temperature inside the bath is at the height at which it is generally used, the mercury column is visible outside the stove. Instead of Kemp's form of stuffing box, B is best made of a piece of brass tube, to which a smaller one, D, is soldered; the sliding tube, c, and the long stem of a are easily adapted by means of perforated corks. The gas enters at c, and finds its way through the open extremity to the long stem of the air thermometer, from which it passes to the burner at D. This burner is conveniently made by brazing two brass tubes in the form of a cross, and so that their bore communicates; the ends being closed, four holes are made with a drill formed from a needle. The dimensions of the burner are such, that each flame is at a distance from the side of the oven equal to a quarter of its linear dimension. This gives great regularity to the heat. A piece of lead, E, cast upon the intersection of the cross, will serve to steady the burner, and to give air to the flame, by

permitting the circulation of air from beneath. A box, four inches in height, upon which the oven rests, encloses the flame; in it an opening, with a movable cover, is left, to light the gas and watch the flame when necessary. The top of the oven has an additional opening, for the insertion of a thermometer, to regulate the heat when adjusting the sliding tube.

Fig. 2 represents the end of the sliding tube in its proper size. The hole, a, through which the gas passes to the burner when the extremity is closed, must be of such a size that merely enough gas passes to prevent the extinction of the light. It is made by heating the tube by a pointed flame, and touching it with a red-hot platinum wire, by which means a small tube may be drawn out, which when broken leaves a small hole; this hole is then melted together in the flame until after trial in the apparatus it is found small enough.

I found no difficulty in keeping within a degree of the temperature required; of course, the delicacy of the apparatus is in proportion to the difference between the contents of the air receiver and the diameter of the long arm of the air thermometer, and owing to increase of pressure, the higher the mercury in this arm the more slowly will it rise by increase of temperature.

For the Journal of the Franklin Institute.

Explosions on board the Steamers Fusileer and Shreveport. By A. C. JONES.

To the Committee on Publications.

GENTLEMEN:-In the early part of January, an explosion took place on board the Attakapas packet Fusileer. It occurred in the Gulf, a short time after leaving the Mississippi river, on her way to Attakapas, and is said to have been caused by gross mismanagement, coupled with drunkenness. The boat was towed to her place of destination, thereby evading an examination into the causes which resulted in the loss of life. This was the first in this vicinity under the new law; and of the second I will now furnish you with the particulars.

The steamer Shreveport, on the 20th, in attempting to back out from a landing on Red river, collapsed the inside flue of the larboard boiler, scalding the second engineer and carpenter, who were aft on duty, and injuring a fireman, who was firing at the time.

The boat has a stern wheel, and the engines and "doctor" are consequently near the stern of the boat, leaving about fifty feet space between them and the after ends of the two boilers. The steam gauge, capable of indicating 200 pounds to the square inch, is connected with the steam pipe above where it branches to the engines. There is here also a supplemental screw valve and pipes for blowing off steam from the boilers through the main steam pipe; this valve had been put on the trip before. A small steam drum connects the two boilers at the after end, the safety valve being over the starboard boiler, and the steam pipe over the larboard one. The accompanying sketch gives the contrivance for either raising or holding the end of the safety valve lever down, and is of the

Toughest description of workmanship. Where it is attached to the end of the safety valve lever, it gives eight leverages, the fixed weight inside of it being 7 to 1. Cords from each end of the bent lever pass through small holes in three wooden cleats, (out of line with each other sideways,) fastened to the carlins above.

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a, end of safety valve lever; b, bent lever, each arm is 8 inches long; c, small rod and cord for holding the lever down; d, first wooden cleat; e, cord for raising lever; f, stancheon through which the bent lever works.

At D, in the sketch, it will be seen that the angle of the cord for holding the lever down is considerable, and yet there is no rounding of the small hole to compensate for this deviation from a straight line; the lines finally pass over two-inch sash pulleys down to the side of the starboard engine. To the end of the cord for holding down the valve, is tied permanently the half of a cam, (about 30 lbs.) Now, one pound on the end of this cord, by its zigzag course and swelling by the wet weather, which has prevailed for some time past, and the roughness of all the parts in connexion with it, will give many pounds on the end of the lever; in fact, to all intents and the purposes of a safety valve, making it useless, the valve being perfectly locked.

This was the first trip of both engineers on this boat, and they were fully provided with certificates from the inspectors of this place, attesting their competency!

The boat had stopped at a landing over fifteen minutes, and steam had been blown off only through the valve mentioned, which is too small for the purpose, as it could not discharge steam as fast as the boilers could make it. They had stopped blowing for about two minutes, and before a part of a turn of the wheels was made to back out, the flue collapsed, and most of the water was discharged aft. The boilers have been about four months in use.

On examination, I found the flue to be flattened nearly vertically its whole length, and lying up against the other flue. It is partly torn off from the after wrought iron head; the other end is half torn off in the lap, a quarter sheet in length from the head, which is much "buckled," apparently by the great pressure on its surface.

The flues are fourteen inches in diameter; the iron is three-sixteenths of an inch in thickness, and is of a medium quality. There is a two inch water space between the flue and the shell. Each boiler has three gauge cocks, the lowest one being about one inch above the tops of the flues; the water line is well defined, and is above the lower gauge cock. That there was plenty of water at the time, is borne out by the appearance of things around, and by the fact of the men at the engines, fifty feet from

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