Part 26 (1/2)

Fig 3 The iron rod 26, 27, which is fixed perpendicular to the center of the bea 7 & 8 The friction-wheels, with the plates of rock-cristal Z, as points of contact by which the friction of the axis of the lever of the balance is avoided

Fig 4 The piece of metal which supports the axis of the friction-wheels

Fig 9 The middle of the lever or bea 10 The theras contained in the jar

When this gazometer is to be used, the cistern or external vessel, LMNO, Pl VIII Fig 1 is to be filled ater to a deterht, which should be the same in all experiments The level of the water should be taken when the beam of the balance stands horizontal; this level, when the jar is at the bottom of the cistern, is increased by all the water which it displaces, and is dihest elevation We next endeavour, by repeated trials, to discover at what elevation the box 28 must be fixed, to render the pressure equal in all situations of the beam I should have said nearly, because this correction is not absolutely rigorous; and differences of a quarter, or even of half a line, are not of any consequence This height of the box 28 is not the sa as this is of one, two, three, or reat order and precision

We next take a bottle which holds eight or ten pints, the capacity of which is very accurately deter This bottle is turned bottom upwards, full of water, in the cistern of the pneu 1 and is set on its lass jar V, having the extremity 11 of the tube 7, 8, 9, 10, 11, inserted into its ree marked by the index 30 upon the sectorthe stop-cock 8, and pressing a little upon the jar A, as much air is forced into the bottle as fills it entirely The degree marked by the index upon the sector is now observed, and we calculate what nuree We then fill a second and third bottle, and so on, in the same manner, with the same precautions, and even repeat the operation several times with bottles of different sizes, till at last, by accurate attention, we ascertain the exact gage or capacity of the jar A, in all its parts; but it is better to have it formed at first accurately cylindrical, by which we avoid these calculations and esti was constructed with great accuracy and uncoineer and physical instrureat number of purposes to which it is applicable; and, indeed, there are many experiments which are almost impossible to be performed without it

It becomes expensive, because, in many experiments, such as the formation of water and of nitric acid, it is absolutely necessary to employ two of the same machines In the present advanced state of chemistry, very expensive and complicated instru the analysis and synthesis of bodies with the requisite precision as to quantity and proportion; it is certainly proper to endeavour to siht by no means to be attempted at the expence of their conveniency of application, and much less of their accuracy

SECT III

_So the voluoing section is too costly and too coenerally used in laboratories for asses, and is not even applicable to every circumstance of this kind

In numerous series of experiments, more simple and more readily applicable methods must be employed For this purpose I shall describe the azometer, and which I still use in preference to it in the ordinary course of my experiments

Suppose that, after an experias, neither absorbable by alkali nor water, contained in the upper part of the jar AEF, Pl IV Fig 3 standing on the shelf of a pneumato-chemical apparatus, of which ish to ascertain the quantity, we ht to which the reat exactness, by means of slips of paper pasted in several parts round the jar If we have been operating inthewater in its stead

This is readily done by filling a bottle quite full of water; having stopped it with your finger, turn it up, and introduce itsdown its body again, the ravity, falls into the bottle, and the water rises in the jar, and takes the place occupied by the mercury When this is accomplished, pour so much water into the cistern ABCD as will stand about an inch over the surface of the9 under the jar, and carry it to the water cistern, Fig 1 and 2 We here exchange the gas into another jar, which has been previously graduated in the e of the quantity or volurees which it occupies in the graduated jar

There is another as, which may either be substituted in place of the one above described, or may be usefully employed as a correction or proof of that ed froraduated jar, turn up the mouth of the marked jar, and fill it ater exactly to thethe water we deter one cubical foot, or 1728 cubical inches, of water for each 70 pounds, French weight

Thejars for this purpose is very easy, and we ought to be provided with several of different sizes, and even several of each size, in case of accidents Take a tall, narrow, and strong glass jar, and, having filled it ater in the cistern, Pl V Fig

1 place it upon the shelf ABCD; we ought always to use the same place for this operation, that the level of the shelf may be always exactly similar, by which almost the only error to which this process is liable will be avoided Then take a narrow rs of water, which corresponds to 10 cubical inches If you have not one exactly of this dier, and di in a little melted wax and rosin This bottle serves the purpose of a standard for gaging the jars Make the air contained in this bottle pass into the jar, and mark exactly the place to which the water has descended; add another ain mark the place of the water, and so on, till all the water be displaced It is of great consequence that, during the course of this operation, the bottle and jar be kept at the same temperature with the water in the cistern; and, for this reason, wethe hands upon either as much as possible; or, if we suspect they have been heated, we ht of the baro this experiment is of no consequence

When the marks have been thus ascertained upon the jar for every ten cubical inches, we engrave a scale upon one of its sides, by raduated in the sa in the mercurial apparatus, only they must be divided into cubical inches, and tenths of a cubical inch The bottle used for gaging these rs of mercury, which exactly corresponds to a cubical inch of that as, byany correction for the difference of height between the surface of the water within the jar, and in the cistern; but it requires corrections with respect to the height of the barometer and ther the water which the jar is capable of containing, up to the marks EF, it is necessary to make a farther correction, for the difference between the surface of the water in the cistern, and the height to which it rises within the jar This will be explained in the fifth section of this chapter

SECT IV

_Of thethe different Gasses from each other_

As experias, it is necessary to be able to separate these from each other, that we may ascertain the quantity and species of each Suppose that under the jar A, Pl IV Fig 3 is contained a quantity of different gasseswith slips of paper, as before directed, the height at which the lass; then introduce about a cubical inch of water into the jar, which will swias contains any as, a rapid and considerable absorption will instantly take place, froasses have, especially the former, to combine with, or be absorbed by water If the water only produces a slight absorption of gas hardly equal to its own bulk, we conclude, that the mixture neither contains as, but that it contains carbonic acid gas, of which water only absorbs about its own bulk To ascertain this conjecture, introduce soas will be gradually absorbed in the course of a few hours; it coas is left almost perfectly free froas

After each experiht at which the mercury stands within the jar, by slips of paper pasted on, and varnished over when dry, that they may not be washed off when placed in the water apparatus It is likewise necessary to register the difference between the surface of the ht of the barometer and theras or gasses absorbable by water and potash are absorbed, water is admitted into the jar to displace thesection, the mercury in the cistern is to be covered by one or two inches of water After this, the jar is to be transported by9 into the water apparatus; and the quantity of gas reraduated jar After this, small trials of it are to be made by experias in question For instance, into a shted taper is introduced; if the taper is not ien gas; and, in proportion to the brightness of the flaas than atmospheric air contains If, on the contrary, the taper be instantly extinguished, we have strong reason to presuas If, upon the approach of the taper, the gas takes fire and burns quietly at the surface with a white flaas; if this flaas; and, if it takes fire with a sudden deflagration, that it is aa portion of the residuuas, red fuas