FORD VAN POINTERS.
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By R. T. Nicholson (Author of "The Book of the Ford ").
IHAVE. often insisted that you should make it a habit to test the' condition of your battery from time to time by use of a hydrometer.; although I know full well that not one Ford driver in a hundred Owns that useful scientific instrument, even if he knows it value. I believe that the reason for this lies mainly in the fact that hydrometers not only have great value, but also command a good price to-day—somewhere about'half-a-guinea--rather chore_ than Iess—and , that half-guineas are none too plentiful in these hard times_ 460.—How to Make Your Own Hydrometer.
So I am going to tell you hew you can make a. serviceable hydrometer for yourself, with very little Fig. 306.—The components of a hydrometer: A, a lobe bulged at its lower end. B, testing the loading in water. C, loaded and coloured and being tested in a liquid of
1.275 'sp. gr. 1), a test tube. E, the barrel .1.of the syringe with its rubber tubing. F, the syringe.
• outlay onthe materials needed. Then there will be no excuse. for you! Mind, I do not claim that the hydrometer that you will make, on my directions, will be quite as good as the one you would buy for halfa-guinea or more ; butI do claim that it will be good enough, and tell you what you particularly want to know as to the condition of your battery.
Shopping.
Go to a chemist—preferably one you know personally, because you want a little friendly help from him. Get him to 'sell you a slight tube of thin glass, closed at one end, open at the other. leis better that the lower half of the tube—that towards the closed end—should be bulged, and the other hall (that towards the open end) should be narrower. (See sketch A.) The whole length of this tube should be about 6 ins. The bore of the narrow half of the tube should be about 71 in., and the bore of the other half should be rather less than in. Exact dimensions, however, are not very important-. Let us call this tube A.
Get the chemistalso to let. you have what he calls . a test tube, 5 ins, long, and of about in. bore—that is to say, a little shorter than tube A, and a little wider than the fatter half of that tube. This is closed and rounded at one end, and open at the other. (See sketch D.)
Next ask the chemist to make you up a liquid of ereactly 1.275 specific gravity: he will know what you mean. You want enough to fill the test tube D, or a little less. The chemist can make the liquid, if he likes, of a mixture of sulphuric acid and water, (It is best to carry this liquid home in a small, clean, dry bottle securely corked, or in the test tube B, similarly corked; but do not let the liquid touch the cork.)
Then buy from the chemist a glass ear-syringe (see sketch F)—a, " male " one. It need not be big or expensive. It should hold as much liquid as will three-quarters fill the test tube D.
All these purchases from the chemist should not cost you so much as half-a-crown ; and a really friendly chemist may not charge you more than a shilling.
Now get an ounce or two of the smallest shot you can buy—as near pin-head size as possible. Further, you want :— A small piece of scaling-wax (red preferred). A few ounces of methylated spirit. Three ol• four inches of tyre valve tubing.
A strip of lubber sheeting. (A piece taken from an old bicycle inner tube will do.) A foot or two of ..fine rubber "cord." (There must be nothing but rubber in it.) Some of these things you will certainly have by you : the cost of the others will not bankrupt you.
You as a Scientific Instrument Maker.
Go home. Drop into tube A as many of your shot as will sink it in ordinary water till it floats upright, with its top end open about I ins: above the surface of the water. You can put the water for the.experiment into test tube D, if you like. Leave the shot in the tube.
Dissolve in methylated spirit enough Sealing-wax to give it good 'colour. The sealing-wax will dissolve readily if you powder it first. You then have a kind of quick-drying varnish. Four the varnish into the tube A (still containing the shot) till it stands about half-way up. the narrow part, completely filling the lower (broader) part. Then set the tube quite uprightin a warm place open end uppermost—the idea being to evaporate all the spirit in the varnish, and
to colour the glass inside up to a point about halfway up the narrow portion of the tube. At the same time, the varnish will cement the shot together so that. they will notshift.
When the varnish is set, see that the tube A is perfectly dry outside. Then thy tube D inside, if still wet with water.
About half fill tube D with the special liquid that the chemist made up for you, and float tube A in this liquid. You will now find that tube A stands higher out of the liquid than it previously stood out of the water. (That is because the specific gravity of the special mixture is higher than that of the water: it is "denser.") It will probably stand so that the-top of the coloured varnish shows slightly above the level of the liquid. If it stands higher, scrape away the varnish till the colour lies flush with the level. You can do this with a rod of metal moistened with methylated spirit pushed down inside the bore, and twisted gently ; but take care not to break the tube. Get the top edge of the colouring matter even and straight. If, on the 'other hand, the top. of the colour stands higher than the level of the liquid, drop sufficient shot into the tube to get the two levels exactly flush. For this purpose, you may have to split a shot in the final adjustment. Added shot must drop down to the bottom of the bulged part of tube A. If the varnish has clogged the passage so that the shot will not pass, clear a way with a. hot hair-pin.
Sealing the Tube.
Your next job is to close the open mouth of the tube A. You do this by putting the open end into the flame of a bunsen burner, turning the tube till the glass is soft. Hold the lower part of the tube with a dry cloth, so as not to burn your fingers. Do not heat more of the•tube than you can help—only the extreme end. You will find the mouth of the tube will close in and seal itself. You must get a tight sealing, so as to keep anything from getting into the tube thereafter, and so upsetting its weight.
When the tube is quite cold, test it once more in your special liquid. It should float with the top of the colour dead flush with, the level of the liquid. (By the way, the special testing liquid should be used for the tests as. soon as possible after it. is made up. Further, it should be kept away from heat.)
Now you have the hydrometer proper—tube A as now furbished.
The Syringe.
You still have to find a means of withdrawing from your battery the electrolytethat you want. to test! Take your glass syringe, pull the plunger right out of the body, and remove the lint and cotton that has been used for winding its lower end—its "piston " proper. That would soon rot away in contact with the electrolyte. You must substitute rubber for it— which will not rot. First build up the "piston " -with a slip of sheet rubber, and wind finally' and evenly with rubber "cord." Do not make the "piston " too tight a fit in the "cylinder," as it
will swell somewhat, and may burst the glass of the body if too tight at first.
Slip on to the nozzle of the syringe three or four inches of valve rubber tubing, and you have your " extractor.'' (The top of the syringe, by the way, is generally closed with a cork pierced centrally where the stem of the ". piston" passes through. Contact with the acid in the electrolyte will gradually rot this cork, although not quickly, as it hardly ever touches the liquid. It is, however, best to scrap the cork, and make a " bearing " for the stem of the "piston" with a strip of inner tube wound round and round till it fits.)
Using Your Hydrometer.
Take the filler cap off one of your cells. Push down the valve tubing on the syringe so that its lower end lies well below the surface of the electrolyte. Lift the plunger of the syringe, and so fill its body well. Squirt this " sample " into your test tube D, in which you have previously placed your hydrometer (the treated tube A). The hydrometer should show its colour line not lower than the surface of the "sample." (You must, of course, hold the test tube quite upright, so that there is no drag of the hydrometer against the walls: of the test tube.) If the hydrometer shows its colour-line higher than the surface of the "sample," your battery is in excellent condition : if the colour-line is below the surface, your battery is in only fair or in poor condition ; and the lower the colour-line lies in relation to the surface of the " sample," the poorer is its condition.
Comparative Drawbacks.
The only disadvantage of this form of hydrometer, as compared with that for which they charge half-a guinea, is that the home-made article is slightly less convenient in use, and that it does not tell you exactly how good, or how bad, the condition of the electrolyte is; but it tells you if it is good or bad, and that is enough.
And if you would like it to tell you a little more, you can make external file marks on tabe A, corresponding with various specific gravities. For instance, get your chemist to make you up extra samples—one of, 1.250 sp. gr. and one of 1.225 sp. gr. Float your hydrometer in the first, note where the level lies on the tube, and make a, fine file mark at that point, which will represent "Fair." Then wipe your hydrometer, and float it in the 1.225 sample, make a second file mark to correspond with its showing, and regard it as representing "Bad.."
But, really, the one marking—that of the colourline—is good enough. All you want to know is whether your battery is or is not fully charged. If it is, all right: if it is not, charge till the colourline shows at. the right level.
Keep the whole apparatus carefully packed away: it is fragile—like all -hydrometers—and will certainly get broken if left carelessly about. Further, keep everything about it scrufinlously clean and dry. Any dirt or moisture on it will upset its showings.
Two cautions :—Do not pour into your battery the special liquids made by the chemist, even though they be composed, like your electrolyte, of sulphuric acid and water. Also always return to it proper cell— not to any other—the electrolyte withdrawn for tests.
I said early in this article that it was best to use a tube A with a bulge at the lower end. It is not absolutely necessary that this bulge should be there, although it is better that it should be, because it makes the hydrometer float better but a piece of, Say, fin, bore will do if you cannot get a bulged tube.
If you are afraid to tackle the job of sealing the open end of tube A, the friendly chemist can easily do it for you.
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