me.

It was found, however, that while it is the best, hitherto contrived, both for precision and ease, there was yet a very minute quantity of alkalies lost by volatilization; and I made further researches to overcome this small loss. This I have successfully accomplished, and for some time I have used an improved form of crucible. The one for half to one gram of silicate, is of the following form and dimensions, viz: an elongated, slightly conical crucible with rounded bottom and cover (either with or without the central wire by which to hold it); length 95 mm.; diameter of opening 22 mm.; diameter of smaller end just at the turn of the bottom 16 mm.; weight about 35 to 40 grams. These are now made by Messrs. Johnson, Mattley & Co., Hatton Garden, London, to whom I have furnished all the necessary directions. This shape is given it in order that the portion of the crucible containing the mixture may be heated strongly, while the upper portion is below a red heat.

Manner of heating the crucible.-The ordinary crucible, if used, may be heated in the manner commonly employed for the fusion of silicates. If the new form of crucible, however, is employed, then the upper part is grasped by a convenient metallic clamp in a slightly inclined position, and a moderate blast from the table blow-pipe made to play upon it for about 25 or 30 minutes. But as gas is to be found in every wellmounted laboratory, Bunsen burners of all dimensions are used, and when properly applied, can be made to give all gradations of heat; a simple, cheap, and convenient furnace, with a properly arranged draught, can be made to accomplish all fusions of silicates without the aid of any manual labor, and I therefore employ such an apparatus. (A description of it is given at the close of this article.)

Method of analysis.--We have now the pure carbonate of lime, granular sal-ammoniac and the proper crucible. The silicate should be well pulverized in an agate mortar;* and half a gram or one gram of it is taken. The former amount is most commonly used, it being sufficient and best manipulated in the crucible; a gram, however, may be conveniently employed. The weighed mineral is placed in a large agate mortar, or better in a glazed porcelain mortar, of half to one pint capacity; an equal quantity of the granular sal-ammoniac is weighed out (a centigram, more or less, is of no consequence), and put into the mortar with the mineral, and the two are rubbed together intimately. After this, add eight parts of the carbon

While in all mineral analysis thorough pulverization of the mineral is usually essential, still it is a singular fact, very good analyses can be made with this method even when the powder is tolerably coarse, and in some experiments with lepidolite, I used powder of which much of it was in particles of from 1-40 to 1 30 of an inch, and obtained excellent results. Notwithstanding this, thorough trituration of the mineral is recommended.

ate of lime in three or four portions, and mix intimately after each addition; empty the contents of the mortar completely upon a piece of glazed paper, that ought always to be under the mortar, and introduce into the crucible. The crucible is now tapped gently upon the table and the contents settled down.

The crucible is then clasped by a metallic clamp in an inclined position, or it is placed in the upper part of the support referred to in the latter part of this article, leaving outside about three-fourths of an inch or one inch. By means of a small Bunsen burner the heat is brought to bear just above the top of the mixture and gradually carried toward the lower part, until the sal-ammoniac is completely decomposed, which takes about five minutes; heat is then applied in the manner suggest ed, either with the blast, or with the burner referred to, acting by its own draught, and the whole kept up to bright red heat, for from 40 to 60 minutes. It is well to avoid too intense a heat.

The crucible is now allowed to cool, when the contents will be found to be more or less agglomerated in the form of a semifused mass. A glass rod or blunt steel point will most commonly detach the mass, which is then dropped into a platinum or porcelain capsule of about 150 centimeters capacity and 60 or 80 centimeters, and distilled water added. After some time, the mass will slack and crumble in the manner of lime; still better, this may be hastened by bringing the contents of the capsule to the boiling point, either over a lamp or water-bath; at the same time, water is put into the crucible to slack out any small particles that may adhere to it, and subsequently this is added to that in the capsule, washing off the cover of the crucible also.

After the mass is completely slacked, the analysis may be proceeded with; as a general thing, I prefer to allow the digestion to continue six or eight hours, though this is not necessary.

If the contents of the crucible are not easily detached, do not use very much force as the crucible may be injured by it, but fill the crucible to about two-thirds its capacity with water, bring it almost to the boiling point, and lay it in the capsule with the upper portion resting on the edge, the lime will slack in the crucible, and then may be washed thoroughly into the dish; also, as before, the cover is to be washed off.

We have now by this treatment with water, the excess of lime slacked into a hydrate, and some of the lime combined with the silica and other ingredients of the silicate in an impalpable form. In solution, there is an excess of chloride of calcium formed in the operation, and all the alkalies originally contained in the mineral, as chlorides. All that now remains

to be done is to filter and separate the lime as carbonate and nothing is left but the chlorides of the alkalies. To do this, proceed as follows: Throw the contents of the capsule on a filter, the best size of which for the quantity above specified, is one 3 to 3 inches in diameter; wash well, to do which requires about 200 centimeters of water; the washing is executed rapidly. The contents of the filter (except in those cases where the amount of the mineral is very small and there is no more for the estimation of the other constituents) is of no use, unless it be desired to heat again to see if any alkali still remains in it. The filtrate contains in solution all the alkalies of the mineral, together with some chloride of calcium and caustic lime; to this solution, after it has been thrown into a platinum or porcelain capsule, is added a solution of pure carbonate of ammonia (an amount equal to about one and a half grams is requir ed). This precipitates all the lime as carbonate; it is not, however, filtered immediately, but is evaporated over a water-bath to about 40 centimeters, and to this is added again a little carbonate of ammonia, and a few drops of caustic ammonia, to precipitate the little lime that is redissolved by the action of the sal-ammoniac on the carbonate of lime; filter on a small filter (2 in.) which is readily and thoroughly washed with but little water, and the filtrate allowed to run into a small beaker. In this filtrate are all the alkalies as chlorides, and a little sal-ammoniac. Add a drop of carbonate of ammonia, to make sure that no lime is present. Evaporate over a water-bath in a tared platinum dish, in which the alkalies are to be weighed; the capsule used is about 60 centimeters capacity, and during the evaporation is never filled to more than two-thirds its capacity.

After the filtrate has been evaporated to dryness, the bottom of the dish is dried, and on a proper support heated very gently by a Bunsen flame, to drive off the little sal-ammoniac. It is well to cover the capsule with a piece of thin platinum to prevent any possible loss by the spirting of the salt; after the sal-ammoniac has been driven off by gradually increasing the heat, the temperature of the dish is brought up to a point a little below redness, the cover being off. (The cover can be cleaned from any sal-ammoniac that may have condensed upon it by heating it over the lamp.) The capsule is again covered, and when sufficiently cooled, and before becoming fully cold, is placed on the balance and weighed. This weight gives as chlorides, the amount of alkalies contained in the mineral.

If the chloride of lithia be present, it is necessary to weigh rapidly, for this salt being very deliquescent takes moisture rapidly.

It not unfrequently happens that the chlorides at the end of the analysis are more or less colored with a small amount of car

bon arising from certain constituents in carbonate of ammonia; the quantity is usually very minute and in no way affects the accuracy of the analysis. In selecting pure carbonate of ammonia for analytical purposes, it is well to take specimens that are not colored by the action of light.

It only remains now to separate the alkalies by the known methods. Under this head I have made several observations, that at some future time may be published as soon as the results are sufficiently definite.

A special arrangement for heating the crucible by gas.-The support and burner, where gas is to be had, are simple in their character and have been contrived after a great variety of experiments with gas furnaces. The figure here given illustrates the stand, burner, crucible, &c., and is about one-sixth the natural size.*

h is the stand with its rod g; d is a brass clamp with two holes at right angle to each other having two binding screws; it

B

slides on the rod g; the second hole is for a round arm attached to b, the binding screw e fixing it in any position. b is a plate of cast iron five to six mm. thick, ten to eleven cm. long, and four and one half cm. broad, having a hole in its center large enough to admit the crucible to within about 15 mm. of the cover, without binding. a is the crucible already referred to which is made to incline a few degrees downward by turning the plate of iron that supports it. c is a chimney of sheet iron, eight to nine cm. long, ten cm. high, the width at the bottom being about 4 cm. at one end, and about three cm. at the other end. It is made with the sides straight for about four cm., then inclines toward the top so as to leave the width of the opening at the top about one cm. A piece is cut out of the front of the chimney of the width of the diameter of the hole in the iron support, and about four cm. in length, being semi-circular at the top, fitting over the platinum crucible. Just above this part of the chimney is riveted a piece of sheet iron in the form of a flattened hook n which holds the chimney in place by being slipped over the top of the crucible support; it serves as a protection to the crucible against the cooling of the currents of air.

*This apparatus can be obtained from T. E. Jenkins & Co., of Louisville, Ky., importers and dealers in chemical apparatus.

f is the burner which has been described in an article on flameheat in this Journal, II, vol. 1, p. 341. The upper opening of it is a slit from 1 to 2 mm. in width, and from 31 to 4 cm. long, and when used is brought within about two em. of the lowest point of the crucible, the end of the flame just playing around the lower end of the crucible; the gas enters the lower part of the burner by two small holes of onesixteenth of an inch, furnishing at one inch pressure about 5 cubic feet of gas per hour; the precaution must be observed already referred to, in heating the crucible at first gently above the mixture. It is surprising to see the effect produced by this simple burner as here used; 8 grams of precipitated carbonate of lime can be decomposed to within two or three per cent in one hour, and when mixed with silica or a silicate, in a very much. shorter space of time; although in my analysis I employ one hour as it requires no attention after the operation is once started. This form of furnace and crucible is found to be convenient for other operations.

Although the details here given are long, the time occupied in the analysis is short, and the necessary precautions are of a simple character, so much so, that results obtained by students in beginning chemical analysis have been found by me far more reliable and less variable on the alkalies of the silicates than on any of the other constituents. Good alkali determinations can be made in three hours or less from the commencement of the operation, hastening the evaporation by more direct application of the heat, which of course requires more close watching

It is a common practice of mine, when a silicate presents itself of which there are no physical means of ascertaining its nature, to make at once an alkali determination, which not unfrequently indicates immediately what it is if it be a known silicate containing an alkali; and if an unknown compound, the analysis made is one step in the examination.

ART. XLI.-On the Great Sun-spot of June, 1843; by Professor DANIEL KIRKWOOD, Bloomington, Indiana.

ONE of the largest and most remarkable spots ever seen on the sun's disc appeared in June, 1843, and continued visible to the naked eye for 7 or 8 days. The diameter of this spot was, according to Schwabe, 74,000 miles; so that its area was many times greater than that of the earth's surface. Now, it has been observed during a number of sun-spot cycles that the larger spots are generally found at or near the epoch of the greatest