the worm, B, which is surrounded by cold water, and finally issues at H as distilled. A baffle plate, F, may be located in the head of the still to prevent any water from being carried over mechanically in case the water in A should boil too violently.

In works where only a limited amount of pure water is required, it is sometimes the practice to condense direct steam from the boilers, or indirect steam that has already been used for heating purposes or otherwise. In this way a comparatively pure water is obtained, but its purity cannot always be depended upon, as oil, which is volatile with steam, is likely to get into it in various ways, and iron rust from steam pipes occasionally causes trouble.

Will you please describe a small still for making distilled water?-H. L. B.

The still is shown in the figure. A still of this kind may be heated by direct gas flame or, what is better, by a steam coil inserted within the still, or by a steam jacket. The figure represents a cross section of such a still. The water in the still, A, is constantly kept at the level of the water in the condenser, B, by means of the cross connection, C. Steam is introduced into the jacket, J, through the valve, D, and escapes through valve E, and by properly regulating these valves, the water in A may be boiled steadily for hours. The vapor passes over through the neck, G, condenses in

Electric Transformer

1: On an alternating current dynamo can a transformer be used to change the high electro-motive force to a high amperage?

2: Can a motor or dynamo be wound with same size wire on the field magnets as that upon the armature, and would you get practical results from this treatment?

3: Please explain what transformers are used for.-H. A.

1: A transformer can be used to change the high electromotive force of an alternating current generator to low electromotive force, the current at the same time being changed from small to large in the same ratio. This is one of the great advantages of alternating current, that its electromotive force can be stepped up or down at will by the transformer, which is cheap, very simple in operation, and very efficient.

to change the electromotive force from a high value to a low value, the primary coil P contains a large number of turns of fine wire, and the secondary a small number of turns of coarse wire. Supposing, for instance, we wish to reduce the voltage from 1,000 to 100; then there will be 10 times as many turns in the primary coil as in the secondary.

TABLE CROQUET BOARD.

2: There would be no particular reason for winding a generator or motor with the same size wire on both the field and the armature, and ordinarily the wire on the armature would be very much larger than that on the fields. This would always be true in the case of a shunt machine. In the case of a series winding, it might happen for some particular work that the design would call for the same size wire on the fields as on the armature, but in case it did so this would be a mere coincidence.

3: The function of the transformer, as already explained, is to vary the electromotive force, the current at the same time varying inversely in the same proportion. If we have a high electromotive force and a low current, this can be changed to a low electromotive force and high current, or vice-versa. The ratio of the secondary electromotive force to the primary is approximately the same as the ratio of the number of secondary turns to the number of primary turns in the transformer.

Table Croquet Set

Take a board that has been well planed, in size 58 by 28 inches. The board must be perfectly level. For a padding for this, in order that the balls may not roll too easily, use burlap or old ingrain carpet. As a bulwark to keep the balls on the board, run a strip all around. Bore holes in the board, each pair of holes being about one inch apart. Stiff copper wire, five inches long, bent into shape, will make excellent arches. Some sort of heavy wood should be used for the mallets. The heads should be onehalf inch in diameter. Fit handles of suitable length, and wind the heads of the mallets with small copper wire. Ordinary marbles may be used for the balls.

Testing Quality of Steel

Can you suggest an acid test for iron and steel?-H. R. J.

The piece of metal to be tested should be filed smooth, or polished. It should then be given a bath in dilute nitric or sulphuric acid for from 15 to 20 hours.

Next it should be washed in water and dried, when certain effects will be manifested according to the grade of the metal. If a frosted effect is produced, the steel is of the best quality; inferior grade has a honey-combed appearance; iron shows a fibrous structure in the direction in which it has been worked.

Preserving Iron

How shall I preserve iron from rusting?— T. A. A.

First immerse the metal for several minutes in a solution of blue vitriol; then place it in a solution of hyposulphite of soda, acidulated with chlorhydric acid. This coating, in color blueish, will protect the iron against all moisture.

Making Nitro-Glycerin How is nitro-glycerin made?-A. H. H.

Ordinary glycerin is sprayed into a vessel containing a mixture of nitric acid and sulphuric acid in the proportion of two parts sulphuric acid to one part A combination of the glycerin with the acids at once takes place with

the result that a scum or cream is formed on the surface. This is carefully skimmed and then washed until all the free acid is removed. The product is a commodity ready for the market.

Railroad Location Survey What constitutes a location survey for a railroad?-R. S. D.

Much of the railroad location of the country has been done by picking out the line on the ground, even making it follow in places the backbone line of the preliminary survey, running from one course to the next by means of suitable curves. In the hands of a good engineer, the method is not necessarily very bad, but it is much improved by the following modification:

The work of the preliminary survey is carefully plotted from the transit notes. and cross-section book to a scale of 200 feet per inch. On this map may be plotted one or more trial location lines. Each of these consists of circular curves joined by tangents. The location line. must pass through any predetermined points and yet join them by lines which will give the best location, considering the conflicting interests. Within the limits of the preliminary map, several locations are generally possible; and one great element of the value of such a map lies in the ease with which several routes may be laid out and compared. Profiles may be drawn for each line laid down, by noting the intersection of the line with each contour. Drawing on the profile the required grade line, will give a relative idea of the amount of earthwork required. The method is especially valuable when "development" is necessary.

Although such a line must sometimes. be laid out by a bold and apparently unsystematic trial of a route, yet some approach to a systematic solution may be made as follows: Assume that the maximum ruling grade has been determined as 1.2 per cent, and that the contours have, as usual, a five-foot interval. It will require 417 feet of 1.2 per cent grade to rise five feet. Set a pair of dividers so that they will step off spaces of 417 feet on the map. Starting on a contour at the required beginning of a grade, swing the dividers so that they will just

reach the next contour, and continue to step off such spaces. Joining these points, such a line would be a purely surface line, would probably be very crooked and otherwise unsuitable, but it probably would be suggestive of a practicable route. After locating on the map the best obtainable line, it should then be transferred to the ground. Measure to scale the lengths of all "tangents" (the straight lines joining the curves), and the radii and

lengths of all curves. Instead of scaling off the length of a curve, it may be more accurate to measure with a protractor, or with a scale of chords, the angle between the tangents at each end of the curve, and from the angle and the radius compute the length. Usually the located line will lie fairly close to the preliminary line-close enough so that tie lines may readily be run between them. These should be scaled from the map. To prevent the accumulation of error due to inaccuracies, the length (or radii) of curves or the length of tangents should be altered if necessary so as to make the location check on the ground with the positions of the stakes of the preliminary survey.

To Make a Ladder

AN ORCHARD LADDER.

I wish to make a light, stout ladder for use in the orchard. I would prefer to construct one of material more durable than pine.— T. H. E.

Spruce and hickory would probably make the best combination for your purpose. The wood should be thoroughly seasoned, care being taken that no warp appear while drying. This is particularly