Volume 40 — HINTS TO CORRESPONDENTS.

No attention will be paid to communications unless accompanied with the full name and address of the writer.

Names and addresses of correspondents will not be given to inquirers.

We renew our request that correspondents, in referring to former answers or articles, will be kind enough to name the date of the paper and the page, or the number of the question.

Correspondents whose inquiries do not appear after a reasonable time should repeat them.

Persons desiring special information which is purely of a personal character, and not of general interest, should remit from $1 to $5, according to the subject, as we cannot be expected to spend time and labor to obtain such information without remuneration.

(1) S. Q.—The speed of a circular saw at the periphery should be from 6,000 to 7,000 feet per minute. The number of revolutions per minute will of course vary with the diameter of the saw.

(2) T. J. F. asks (1) for the best way to fasten emery on a wooden wheel, to be used in place of a solid emery wheel. A. Cover the wheel with leather devoid of grease, and coat the leather surface, a portion at a time, with good glue; immediately roll the glued surface in emery spread out on a board. 2. How can I fasten small pieces of looking glass on iron? A. Use equal parts of pitch and gutta percha mixed together.

(3) W. C. asks: 1. What is the power of the simple electric light described in Supplement No. 149? A. When supplied with a strong current it is equal to 5 or 6 5-foot gas burners. It is designed for temporary use only. 2. What is the cost of manufacturing the dynamo-electric machine in Supplement No. 161? A. The one shown in the article referred to cost about $35.

(4) L. D. asks: 1. Which is the better conductor, silver or copper? A. Silver. 2. And the comparative resistance offered to the electric current by water and the above? A. Taking pure silver as 100,000,000, the conductivity of distilled water would be 0.01.

(5) H. J. F. writes: In Supplement 162 a simple electric light is described. I wish to light a room 20x20x10 feet. 1. How large is the bell glass? A. 2½ inches. 2. Can I use battery carbon? A. Use a carbon pencil made for electric lamps. 3. How can I make tray water tight after putting wire through? A. With gutta percha. 4. I have one large cell Bunsen and one Smee. How many more and of what kind shall I get? A. One of the batteries described in Supplements 157, 158, 159, will do, probably 8 or 10 Bunsen elements would be the best.

(6) W. B. F. writes: I tried to make an electric pen, like the one described in your Scientific American, of February 22d, 1879, using a Smee's battery, a circuit breaker, and an induction coil, but it did not work. Is there anything wrong, or is a condenser different from an induction coil? A. A condenser consists of a number of sheets of tin foil separated from each other by larger sheets of paper. One half of the tin foil sheets are connected with one terminal of the primary coil, the other half with the other terminal; the tin foil sheets connected with one terminal alternate with those of the other terminal. The condenser is essential to the working of the coil. For complete directions for making induction coils, see Scientific American Supplement No. 160.

(7) J. De F. asks: 1. Knowing the resistance of a wire of given conductivity, length, and diameter, will the resistance of any other wire be in proportion inversely? A. Yes. 2. Is there heat enough developed in the secondary coil of an induction coil to prevent the use of paraffine as an insulating material? A. With proper battery power, no. 3. How high in the list of non-conductors does paraffine stand? A. It is one of the best. 4. Will a cotton insulator soaked in paraffine answer as well as silk? A. No, because it renders the covering of the wire too thick. 5. Can you recommend any insulating material for making induction coils which will dry rapidly? A. Alcoholic shellac varnish. Rosin to which a little beeswax has been added is an excellent insulator; it must be applied in a melted state. 6. What is the composition of the black material covering the Leclanche porous cell? A. Gutta percha. 7. Is the magneto-electric machine described in the Scientific American Supplement patented? A. To which do you refer? Most, if not all of them are patented.

(8) B. V. F. writes: With reference to item 8, on page 139, of Scientific American, March 1, 1879, I think there is some mistake about the coal you think required to heat 1,000 cubic feet space. I burn some 8 tons coal to heat, in the whole year, such part of my house as must exceed 25x20x18=9,000 cubic feet. We keep up a moderate heat at night. Ventilate more than most families do; take part only of the cool air, and only in part of the coldest weather, from the cellar, which at such times is opened into the main entries. House wood, back plastered, and stands alone. If 100 lbs. coal would heat 1,000 feet one day, I ought to burn 900 lbs. a day, or nearly 14 tons in December and 14 more in January. A. We are glad to receive these data, which correspond quite closely with some obtained by recent accurate experiments. The estimate given in the Scientific American also agrees well with experiments on the use of hot air heaters for very small buildings or rooms. Of course, the larger the space to be heated, the more economically it can generally be done.

(9) W. M. S. asks: Will the coil described in Supplement No. 160 do for the electric pen described in a recent number of the Scientific American? If not how must it be changed? A. It is too large; make it one half the size given.

(10) B. G.—In reply to your inquiry as to Mr. Stroh's telephone experiment, we give the following, which we clip from the English Mechanic: A singular experimental effect, of special interest just now from its possible bearing on the theory of the source of sound in the Bell telephone, has just been observed by Mr. Stroh, the well known mechanician. If a telephone, T, with the circuit of its coil left open, be held to the ear, and a powerful magnet, M, be moved gently up and down along the length of the magnet, as shown by the arrow, and at a distance of an inch or two from it, a faint breathing sound will be heard, the recurring pulses of sound keeping time with the up and down motion of the magnet. The sound may be aptly compared to the steady breathing of a child, and there is a striking resemblance between it and the microphonic sounds of gases diffusing through a porous septum as heard by Mr. Chandler Roberts. We understand that Professor Hughes is investigating the cause of this curious sound by help of the microphone.

(11) "Enterprise" asks: What part of its volume will iron expand in passing from a temperature of 60° to melting temperature? A. The cubical expansion of iron for each degree (C.) between 0° and 100° is 0.00003546 of its volume, its volume being 1. This ratio however, increases somewhat at higher temperatures, since the mean coefficient of expansion for each degree between 0° C. and 300° C. is 0.00004405. The question you ask has probably never been settled. You may form an approximation by the use of the above ratios, knowing the melting point of the iron.

(12) P. L. O. asks for a good chemistry for a beginner to study without a teacher. A. Fownes' "Chemistry;" Gorup-Besanez, "Inorganic, Organic and Physiological Chemistry."

(13) L. E. M. asks: What is the best method of keeping fine guns from rusting, and what oil should be used? A. For the outside, clear gum copal 1 part, oil of rosemary 1 part, absolute alcohol 3 parts. Clean and heat the metal and apply a flowing coat of the liquid by means of a camel's hair brush. Do not handle until the coat becomes dry and hard. For the inside of the barrel a trace of refined sperm oil is as good as anything, but an excess should be avoided.

(14) A. H. B. asks how much weight, falling 10 feet, will be required to produce one horse power for five hours? A. One horse power for 5 hours = 33,000 × 300 = 9,900,000 foot pounds—so that the weight required is 9,900,000 ÷ 10 = 990,000 lbs.

(15) A. D. R. asks: 1. In renewing a Leclanche battery, do the zincs have to be amalgamated? A. They are usually amalgamated. 2. Will two cells large size Leclanche battery give any light, using the simple lamp described in Supplement No. 162? A. No.

(16) H. L. J. writes: In a recent issue of the Scientific American you state that the floating of solid iron on melted iron is on the same principle as the floating of ice in water. I do not quite understand how it can be. Please explain. A. Solid iron, at an elevated temperature, floats upon molten iron for the same reason that ice floats upon molten ice-water—because it is specifically lighter. You will find the subject discussed at length in Tyndall's "Heat as a Mode of Motion."

(17) J. W. will find full directions for canning corn, etc., on p. 394 (4), vol. 39, Scientific American.

(18) "Amateur" writes: I wish to make some small bells that have a clear ring. What metal or metals can I use that I can melt easily? A. Use an alloy of tin and antimony. See Scientific American Supplement No. 17.

(19) H.—A nutritious mixed diet is unquestionably the best, care being taken to avoid an excess of meat.

(20) W. F. writes: I have made an engine, and would like to find out what size of boiler it will require. The cylinder has 2¼ inch bore and 3 inches stroke. A. It depends upon pressure and speed to be maintained; probably a vertical tubular boiler, 15 inches diameter, and 32 to 36 inches high, would suit you.

(21) R. G. (Salt Lake).—Please send full name.

(22) J. M. G. asks: If two persons each pull one hundred pounds on opposite ends of a rope, what will be the strain on the rope? A. The strain on the rope will be 100 lbs.

(23) W. M. M. asks: In laying off a mill stone in furrows, what draught is given? What amount of the space of a stone is given to furrows and what to grinding surface? A. There is considerable difference in the practice of various millers, and we would be glad to receive communications from those experienced in the art of dressing millstones.

Minerals, Etc.—Specimens have been received from the following correspondents, and examined, with the results stated:

S. (New Orleans.)—The powder consists of a mixture of zinc oxide and finely powdered resin. A quantitative analysis would be necessary to determine the proportions.

Any numbers of the Scientific American Supplement referred to in these columns may be had at this office. Price 10 cents each.

COMMUNICATIONS RECEIVED.

Life Preserving Stone. By J. D. W. On Ventilation. By D. W. What is Mental Action? By N. K. Panama Railroad or Canal. By G. R. P. A Problem. By K. On the Gary Motor. By G. F. M. Magnetic Motor. By G. W. W., W. A. A., G. H. F. House Warming. By H. B. F. The Injector. By M. A. B. Columbus' Problem; Cure for Diphtheria; The Mullein Cure for Consumption. By R. W. L. A Visit to Tula. By L. R. On Vacuum in Pumps and the Atwood Machine. By P. J. D. On the Patent Bill. By R.

[OFFICIAL.]

INDEX OF INVENTIONS

FOR WHICH Letters Patent of the United States were Granted in the Week Ending February 18, 1879, AND EACH BEARING THAT DATE.

[Those marked (r) are reissued patents.]

A complete copy of any patent in the annexed list, including both the specifications and drawings, will be furnished from this office for one dollar. In ordering, please state the number and date of the patent desired, and remit to Munn & Co., 37 Park Row, New York city.

Air heater, W. Pickhardt212,499

Anchor, A. F. White212,340

Animal trap, S. J. Bennett212,430

Axle box, vehicle, P. K. Hughes212,382

Axle, carriage, C. H. Kendall212,387

Axle for wagons, trussed, J. Herby212,378

Axle, vehicle, C. H. Kendall212,386

Barrel cover, C. Brinton212,350

Bed bottom, J. Flinn212,451

Bed bottom, spring, W. B. Crich212,443

Bedstead, sofa, A. N. Hornung212,312

Bedstead, wardrobe, H. P. Blackman212,348

Belt hook templet, E. Card212,353

Boot and shoe laster, L. Graf212,460

Boot and shoe sole polisher, etc., O. Gilmore212,372

Boot and shoe sole edge trimmer, C. H. Helms212,311

Boot fronts, cutting in, C. H. Colburn212,357

Boot, India-rubber, G. Watkinson (r)8,587

Bottle filler, W. S. Paddock212,494

Bread board, H. Van Doren212,334

Brick, shed for drying, C. H. Roselius212,511

Bridge gate, A. Stempel212,329

Broom corn tabler, G. W. Foulger212,454

Button F. E. Williams212,418

Calculator, tax, P. F. Pettibone212,498

Car coupling, G. R. Hamilton212,462

Car coupling, S. A. Haydock212,464

Car coupling, J. Worrall212,529

Car heaters, coupling for pipes of railway, J. W. Graydon212,376

Car heater, railway, J. W. Graydon212,375

Car heating pipe coupling, railway, J. W. Graydon212,374

Car ventilation, J. Knipscheer212,475

Cars, heating, J. & J. W. Russell212,403

Cars, supplying water to wash stands on, D. H. Jones212,385

Carbureter feed regulator, W. H. Reed212,502

Card machine burr conveyer, W. C. Bramwell212,435

Carpet beater, J. L. Leach212,476

Carriage, C. H. Palmer, Jr.212,397

Carriage bow, F. H. Niemann212,491

Carriage, child's, F. H. Way (r)8,583

Carriage top prop, J. P. Simpson212,519

Carriage canopy top, D. Gleason212,458

Cartridge, W. W. Hubbell212,313

Chair foot or leg rest, M. E. Keiran212,474

Chimney, locomotive engine, H. R. Walker212,414

Chuck, lathe, J. H. Vinton212,413

Churn power motion, W. F. Witherington212,527

Cigarette, C. C. Millaudon212,392

Coat, reversible, N. H. Lund212,479

Cock and faucet, etc., self-closing, J. Broughton212,436

Coffee pot, teapot, etc., stand, D. H. Murphy212,395

Coffee roaster, R. Davis212,445

Corset, W. Thomas212,411

Corset steel, E. M. Smith211,520

Dental plugger, W. G. A. Bonwill212,434

Door securer and combined tool, P. E. Rudel212,512

Door sill and carpet strip, S. M. Stewart212,521

Drip pan and self-oiler for bearings, R. B. Eason212,449

Egg cup and opener, D. H. Murphy212,394

End gate, wagon, W. H. Parkin212,398

File, bill, E. H. Owen212,493

Files, recutting, M. J. Murphy212,490

Filter, J. W. Lefferts212,477

Firearm, breech-loading, H. Goodman212,459

Firearm lock, Kaufmann & Warnant212,473

Fire extinguisher, D. T. Perkins212,322

Fires in buildings, extinguishing, C. Barnes212,346

Fluid motor, Chase & Bowker212,356

Fountain tip, H. G. Fiske212,368

Furnace, G. B. Field212,366

Game apparatus, W. T. Ebert212,304

Garter, etc., clasp, L. Lobenstein212,390

Gate, McKinley & Ellis212,482

Gate, G. W. Pyle212,501

Glassware, decorating, H. Feurhake212,365

Glassware shaper and finisher, Atterbury & Beck212,421

Glazier's tool, W. H. G. Savage212,515

Governor and friction brake for machinery, speed, T. A. Weston212,337

Grain drill, C. F. Davis (r)8,589

Harness breeching strap, H. Holt212,467

Harrow, toothless, J. W. Mulvey212,393

Harvester, W. A. Wood212,528

Harvester cutter, B. Pratt212,323

Harvester, grain binding, J. F. Appleby212,420

Harvester reel, B. Moreland212,318

Harvesting machine, Dutton & Tornquist212,303

Hat formers, web tender for, R. Eickemeyer212,450

Hay binder and elevator, P. H. Nichols212,319

Hay elevator, H. Barlow212,427

Hay tedder, E. J. Knowlton212,388

Headlights, signal for locomotive, W. Kelley (r)8,591

Heat regulator for furnaces, A. C. Norcross (r)8,582

Hoisting bucket, F. H. C. Mey212,317

Hoisting drums, etc., friction brake and clutch for, T. A. Weston212,338

Hoisting machine, T. A. Weston212,339

Horse toe weight, G. C. Clausen212,440

Hydrant, J. Snell212,408

Hydrant, street, G. C. Morgan212,486

Hydraulic motor, W. S. Puckett212,500

Injector, steam boiler, G. R. Buckman212,438

Keg trussing machine, E. & B. Holmes212,381

Kettle, H. C. McLean212,483

Kitchen cabinet, C. A. Adams212,343

Lamp, J. H. Irwin212,470

Lamp burner, E. B. Requa212,401

Lamp, fountain, C. Stockmann212,522

Lamp shade holder, Brown & Taplin212,437

Lamp, street, J. Stewart212,410

Lamp wick, H. Halvorson212,309

Life preserver, T. Richards212,402

Life preserver, R. E. Rose212,404

Lock, W. E. Forster212,452

Lock gate, D. Risher, Jr.212,506

Mechanical movement, C. B. Hitchcock212,380

Metal tube maker, A. Ball212,425

Middlings separator, J. Schoonover212,406

Milker, cow, A. C. Baldwin212,423

Millstone adjustment, S. P. Walling212,525

Millstone curb or hoop, J. S. Detwiler212,361

Miter machine, J. J. Spilker212,409

Mop head, H. Murch212,489

Needle eye polisher, George & Payne212,455

Oil cup, F. Lunkenheimer212,480

Ore concentrator, E. W. Stephens212,330

Ore roaster, C. E. Robinson212,508

Oven bottom and slide, J. Jewett212,471

Oysters, board bank for fattening, F. Lang212,389

Package or box filler, Bolton & Strieby212,349

Paper cutter, J. M. Jones212,384

Paper folder, R. M. Hoe212,466

Paper machines, method and apparatus for producing a vacuum in the suction box of, Dunn & Hollister212,362

Paper machines, wire guide for J. W. Moore212,485

Paper making, treating pulp stock, S. & J. Deacon212,447

Paper scorer and cutter, G. L. Ingram212,314

Paper scorer and cutter, W. F. Lodge212,315

Permutation lock dial screen, Corbett & Miller212,359

Picture exhibitor, A. L. High212,465

Pill machine, Fort & Moore212,453

Pipe wrench, S. W. Hudson212,468

Pipe wrench with cutter, Franklin & Gilberds212,369

Plant protector, E. R. Frederick212,306

Plants, etc., poison distributer for, G. Townsend212,412

Planter and drill, check row, G. J. Hyer212,469

Planter, corn, J. A. Roderick212,509

Plow, E. Walker212,524

Plow attachment, A. O. Bement212,429

Plow cutter, A. Aldrich212,419

Plow, sulky, J. R. Whitney212,341

Printer's roller, T. M. Fisher212,367

Printing machine, L. C. Crowell212,444

Pumping engine, duplex, G. F. Blake (r)8,585

Radiator for steam heaters, Covert & Snyder212,360

Railway crossing, Bernard & Perkins212,432

Railway switch, C. F. Gessert212,456

Ratchet mechanism and clutch for machinery, T. A. Weston212,336

Rocking chair, J. W. Hamburger212,461

Rotary engine, A. B. Haughey212,463

Rubber mat, E. L. Perry212,497

Sad iron holder, A. Failor212,363

Safety pin, I. W. Stewart (r)8,592

Salt cellar, W. Sellers212,518

Sandpaper roll, O. Gilmore212,371

Sash cord guide, Clarkson & Kesler (r)8,586

Sash fastener, J. Benson212,431

Sash fastener, G. W. Cary212,354

Sash fastener, J. B. Morris212,487

Saw, circular, G. Schleicher212,516

Saw handle, E. R. Osgood212,396

Saw, jig, G. W. Gary212,355

Saw mill, gang, H. D. & E. N. Wickes212,526

Saw mill head block, J. T. James212,383

Sawing machine, scroll, N. P. Selden212,326

Scales, platform, F. Fairbanks212,364

Scales, weighing, G. L. C. Coulon212,300

Scarf pins, etc., making ball heads of, J. N. Allen212,297

Scythe snath fastening, P. E. Rudel212,513

Sewer trap, J. P. Cahill212,352

Sewing implement, A. J. Lytle212,481

Sewing machine, C. O. Parmenter212,495

Sewing machine attachment, J. B. Sulgrove212,523

Sewing machine plaiter, White & Bowhannan212,417

Sheet metal vessel bottom, F. W. Moseley212,484

Shoe, Searl & Bly212,517

Skate, C. T. Day (r)8,590

Skylight, J. Friend212,307

Slate frame, E. Butler (r)8,588

Sled propeller, G. F. Shaver (r)8,593

Smelting furnace, iron, P. L. Weimer212,415

Sole edge burnisher, T. P. Young212,342

Spoke tenoning machine, A. J. Roberts212,507

Sprinkling can, G. F. Payne212,321

Stamp, postage and revenue, K. Wheeler212,416

Staple machine, W. M. Collins212,441

Staples in paper, etc., device for inserting metallic, G. W. McGill212,316

Stave crozer and chamferer, H. H. Dunlevy212,448

Steak tenderer, E. Richmond212,505

Steam boiler, fire tube, J. Cowhig212,301

Steam brake for locomotives, etc., W. L. Card212,439

Steam piping for heating, etc., B. F. Osborne212,420

Steam trap, I. W. Merrill212,391

Stove and furnace grate, S. Smyth212,407

Stove, cooking, G. H. Hess212,379

Stove, cooking, J. Jewett212,472

Stove, oil, Fleming & Hamilton212,305

Stove oven door and shelf, C. W. Brieder212,351

Strainer, gravy, J. Scheider (r)8,584

Strap for garments, adjusting, T. O. Potter212,400

Street motor, J. T. Cord212,442

Surveying instrument leveler, G. N. Saegmuller212,405

Swing, J. Ryan212,514

Telephone apparatus, speaking, E. Gray212,373

Telephony, electric, Black & Rosebrugh212,433

Telephony, electric, A. M. Rosebrugh212,510

Thill coupling, D. C. Bacon212,422

Thill coupling, C. E. Gillespie et al.212,308

Thill coupling, M. F. Ten Eyck212,333

Thill supporter, vehicle, H. O. Rector212,325

Ticket, passenger, J. H. Purdy212,324

Tiles for use as stands, frame for holding ornamental or fancy pottery, C. A. Wellington212,335

Tiles, decorative, J. G. Low212,478

Tiles, paving blocks, etc., composition for drain, W. H. Haight212,377

Tire upsetter, B. K. Taylor212,332

Tobacco, curing, A. P. Poladura212,399

Tobacco cutter, Bauer & Seitz212,347

Tobacco flavoring compound, D. Sternberg212,331

Tobacco manufacture, J. T. Harris212,310

Tobacco presser, F. B. Deane212,446

Traction engine, J. Cooper212,358

Truss, J. R. Alexander212,344

Type distributer, A. C. Richards212,503

Type setter, A. C. Richards212,504

Umbrella, M. Girbardt212,457

Umbrella runner, W. H. Belknap212,428

Undershoe or slipper, G. Gardner212,370

Vehicle seat lock, W. G. Allen212,345

Vehicle spring, M. H. Crane212,302

Vehicle spring bolster, J. G. Snyder212,328

Velocipede, E. C. F. Otto212,492

Wash boiler, F. J. Boyer212,299

Washing and bath tub, J. B O. Shevill212,327

Washing machine, J. W. Patterson212,496

Water meter diaphragm, W. B. Mounteney212,488

Whip holder, Curtis & Worden (r)8,581

Wire measurer and cutter, G. A. Baron212,426

Wire, winding tubes and rods with, A. Ball212,424

Wrench, C. B. Billings212,298

TRADE MARKS.

Boots, shoes, and brogans, W. F. Thorne & Co.7,037

Cigars, Sullivan & Burk7,035

Cigars, cigarettes, and smoking and chewing tobacco, B. Hilson7,038

Cotton gins, Printup, Brother & Pollard7,042

Fertilizers for flowers, W. H. Bowker & Co.7,041

Grain fans, J. Montgomery7,032

Hair goods for ladies' wear, M. E. Thompson7,040

Hoes, Semple & Birge Manufacturing Company7,039

Medicine for the cure of neuralgia, and the like diseases, J. S. Nicolds7,033

Roofing paper, carpet paper, or paper felt, and building paper, Watson & Janes7,043

Soap, Gallup & Hewitt7,036

Spool cotton, J. & J. Clark & Co7,031

Table cutlery, John Russell Cutlery Company7,034

DESIGNS.

Carpet, T. J. Stearns11,029

Combined sleigh bell and terret ring, H. M. Richmond11,027

Crocheted body for shawls, L. Howard11,028

Oil cloth, C. T. & V. E. Meyer11,024 to 11,026

Statue, A. Bartholdi11,023

English Patents Issued to Americans. From February 18 to February 21, inclusive.

Bed bottoms, etc.—C. D. Flynt, Brooklyn, N. Y. Berth.—D. Huston, Boston, Mass. Lead smelting furnace.—G. T. Lewis, Philadelphia, Pa. Locks.—A. P. Thomas et al., Baltimore, Md. Railway joint.—P. T. Madison, Indianapolis, Ind. Spikes for railroads.—R. Bocklen, New York city. Ventilating buildings.—F. S. Norton, New York city.