in the test solution, the process may be declared finished. and the main solution should be allowed to settle, after which the clear portion is carefully poured off. The sediment, consisting of zinc oxide and perhaps impurities. contained in that metal, is not desirable in a working solution for soldering. True, work can be done with dirty soldering acid or other fluid, but better work can be done with clean solutions, as well as surfaces, and tools.

PUBLICATIONS OF

The Derry-Collard Co.

NEW YORK.

PRACTICAL PAPER SERIES

TURNING AND BORING TAPERS.

Fred H. Colvin.

A plainly written explanation of a subject that puzzles many a mechanic. This explains the different ways of designating tapers, gives tables, shows how to use the compound rest and gives the tapers mostly used.

DRAFTING OF CAMS.

Louis Rouillion.

(25c.)

The laying out of cams is a serious problem unless you know how to go at it right. This puts you on the right road for practically any kind of cam you are likely to run up against. And it's plain English, too. (25c.)

COMMUTATOR CONSTRUCTION.

Wm. Baxter, Jr.

The business end of a dynamo or motor is the commutator, and this is what is apt to give trouble. This shows how they are made, why they get out of whack and what to do to put 'em right again. (25c.)

THREADS AND THREAD CUTTING.

Colvin-Stabel.

This clears up many of the mysteries of thread cutting such as double and triple threads, internal threads, catching threads, use of hobs, etc. Contains a lot of useful hints

A complete course of instruction in all kinds of hard and soft soldering. Shows just what tools to use, how to make them and how to use them. (25c.)

WIRING A HOUSE.

Herbert Pratt.

Shows every step in the wiring of a modern house and explains everything so as to be readily understood. Directions apply equally to a shop. (25c.)

MACHINE SHOP ARITHMETIC.
Colvin-Cheney.

Most popular book for shop men. Shows how all shop problems are worked out and "why." Includes change gears for cutting any threads; drills, taps, shink and force fits; metric system of measurements and threads. Used by all classes of mechanics and for instruction by Y. M. C. A. and other schools. Fourth edition. (50c.)

BEVEL GEAR TABLES.

D. Ag. Engstrom.

No one who has to do with bevel gears in any way should be without this book. The designer and draftsman will find it a great convenience, while to the machinist who turns up the blanks or cuts the teeth, it is invaluable, as all needed dimensions are given and no fancy figuring need be done. ($1.00.)

PRACTICAL PERSPECTIVE.

Richards-Colvin.

Shows just how to make all kinds of mechanical drawings in the only practical perspective isometric. Makes every`thing plain so that any mechanic can understand a sketch or drawing in this way. Saves time in the drawing room and mistakes in the shops. Contains practical examples of various classes of work. (50c.)

CHANGE GEAR DEVICES.
Oscar E. Perrigo.

A book for every designer, draftsman and mechanic who is interested in feed changes for any kind of machines. This shows what has been done and how. Gives plans, patents and all information that you need. Saves hunting through patent records and reinventing old ideas. A standard work of reference. ($1.00.)

HOW TO BUILD AN AUTO.

F. C. Mason.

Gives exact instruction to any mechanic who wishes to build a modern runabout or touring car on approved lines. Full designs and dimensions are given of motor and car, and many have been built. By a designer and mechanic, and is thoroughly practical in every way. ($1.00.)

AMERICAN STEEL WORKER.

E. R. Markham.

The standard work on hardening, tempering and annealing steel of all kinds. A practical book for the machinist, tool maker or superintendent. Shows just how to secure best results in any case that comes along. How to make and use furnaces and case harden; how to handle highspeed steel and how to temper for all classes of work. Second edition. ($2.50.)

ENGINEERS ARITHMETIC.

Colvin-Cheney.

A companion to Machine Shop Arithmetic, arranged for the stationary engineer. Shows how to work the problems of the engine room and shows why." Has steam tables and a lot of other useful information that makes it popular with practical men. (50c.)

AMERICAN STATIONARY ENGINEERING.

W. E. Crane.

A new book by a well-known author. Begins at the boiler room and takes in the whole power plant. Contains the result of years of practical experience in all sorts of engine rooms and gives exact information that cannot be found elsewhere. It's plain enough for practical men and yet of value to those high in the profession. Has a complete examination for a license. ($2.00.)

SWITCHBOARDS.

Wm. Baxter, Jr.

The only book dealing with this important part of electrical engineering. Takes up all sizes and kinds from the single dynamo in the engine room to the largest power plant work. Includes divert and alternating currents; oil

switches for high tension; arc and incandescent lighting; railway work, and all the rest, except telephone work. ($1.50.)

LINK MOTIONS, VALVES AND VALVE SETTING.
Fred H. Colvin.

A handy little book for the engineer or machinist that clears up the mysteries of valve setting. Shows the different valve gears in use, how they work and why. Piston and slide valves of different types are illustrated and explained. A book that every railroad man in the motive power department ought to have. (50c.)

TRAIN RULES AND DISPATCHING.

H. A. Dalby.

Contains the standard code for both single and double track and explains how trains are handled under all conditions. Gives all signals in colors, is illustrated wherever necessary, and the most complete book in print on this important subject. Bound in fine seal flexible leather. pages. ($1.50.)

AMERICAN COMPOUND LOCOMOTIVES.

Fred H. Colvin,

221

The latest and most complete book on compounds. Shows all types, including the balanced compound which is now being used. Makes everything clear by many illustrations and shows valve setting, breakdowns and repairs. A handsome book with ten special inserts of locomotives. ($1.50.)

THE RAILROAD POCKETBOOK.

Fred H. Colvin.

Different from any book you ever saw. Gives clear and concise information on just the points you are interested in. It's really a pocket encyclopaedia, fully illustrated, and so arranged that you can find just what you want in a second without an index. Whether you are interested in Axles or Acetylene; Compounds or Counter balancing; Rails or Reducing Valves; Tires or Turn-tables, you'll find them in this little book. It's very complete. Flexible cloth cover. 250 pages. ($1.00.) (Interleaved with ruled pages for notes, $1.50.)