968

WATER. —Organic Carbon and Nitrogen.

with coarse oxide to a distance of about 270 m.m.from the closed end. Next introduce a plug ofmetallic copper gauze, made by tightly rolling a slipof fine copper gauze (free from zinc), 80 m.m. wide,round a copper wire, and covering the compactcylinder thus formed with an outer case of ratherthin sheet copper, the edges being made to meetwithout overlapping. The diameter when finishedshould be such that it fits easily into the combustiontube. A number of these cylinders are put into apiece of combustion tube, heated to redness in thefurnace, oxidised superficially by passing a cur-rent of air through the tube, and the oxide thusformed then reduced to the metallic state by sub-stituting dry hydrogen for the air, the current ofhydrogen being continued during the cooling of thetube. The copper cylinders should be preserved ina stoppered bottle. They may be used two or threetimes, and should then be again heated in a currentof hydrogen, and so on.

After inserting the copper plug, introduce about20 m.m. in length of coarse oxide in order to oxidiseany traces of carbonic oxide which may have beenproduced by impurities in the copper gauze. Drawoff the open end of the tube before the blow-pipe,to form a neck about 100 m.m. in length and 4 m.m.in diameter ; smooth the end where cut off by heat-ing it in the blow-pipe flame, and bend the neck atright angles. It is then placed in the combustionfurnace, care being taken so to arrange it that thewhole of the contents of the tube can be, whendesired, heated to redness.

To exhaust the tube in the first instance, andafterwards to remove and collect the gaseous pro-ducts of the combustion, the Sprengel mercury pumpis employed, a convenient form of which is shown inFig. 3. The glass funnel, a, is filled with mercury,and is connected by means of a short eaoutchouotube, on which is a screw, e, pinch-cock, b, witha long narrow tube extending nearly to thebottom of the outer tube, d, which is about 900m.m. in length and about 10 m.m. in internaldiameter, and is secured in the neck of the glassfunnel, c, by means of plaster of Paris. Thissupply tube is connected by means of a longer pieceof caoutchouc, which, to withstand the internalpressure of mercury, must be covered closely with astrong sheath of canvas or tape, with the mercurypump proper. A screw pinch-cock on the caout-chouc tube controls the flow of mercury through it.The ascending limb of the pump, fg, consists of acommon narrow glass tube, and is about 600 m.m.in length. At g it is fused on to a piece of thicktube with a bore of 1 m.m. and 1500 m.m. in length,which is bent on itself at h, whilst at the open end,k, it is curved sharply upwards. At % a shortpiece of tube, similar to / g, is fused in, openat the top and carrying on it a wider glycerintube, l , which slides up and down on the narrowtube by means of a caoutchouc stopper. At l thebent connecting tube, l m n, is attached by a shortcaoutchouc tube, so that the wider tube filled withglycerin can be pushed up over the joint, which is

thus entirely immersed in glycerin, and leakage of airinwards effectually prevented. The connecting tubehas a bore of 1 m.m., and has a small bulb blown on

Fig. 3.

it at m, and carries at its end a wider tube, n, whichcan be filled with water to cover the joint by whichthe combustion tube, o, is attached. Glycerin isused in l, as that joint is seldom detached, and isintroduced merely to give flexibility to the apparatus.The two limbs of the tube, f g, are firmly lashedtogether at two points, the tubes being there coveredby short pieces of caoutchouc tube to preventfracture. The funnels, a and c, rest in ring sup-ports, but the pump, f h k, rests entirely on theend k; the upper part being held in a forked guidein which it is free to move towards or from thecombustion furnace.

The pump may stand in a porcelain or woodenmercury trough of any convenient form. Whentwo pumps are employed a convenient form oftrough is that shown at B; where t is a deep chan-nel having two recesses, u u, communicating withit to receive the pumps, the recurved ends of thesebeing towards the channel, t. The test tubes inwhich the gases are collected are filled with mercuryin the channel, t, and are then inverted over theends of the pumps, and are kept upright in therecesses by little wire gates, v v, across the entrances.At w is a well 90 m.m. deep and 42 m.m. indiameter; the channel, t, is 75 m.m. deep and 25m.m. wide; the recesses are 40 m.m. long, 25 m.m.wide, and 75 m.m. deep; the shelf, s, is 50 m.m.deep. The whole is cut out of a solid piece ofmahogany and stands on four short legs, so thatmercury can readily be drawn off from it to thelevel of the shelf, s, by means of the pinch-cock, b.

In the furnace the tube rests in a trough of sheet