"The pump, shown in Figure 1, is constructed almost entirely of brass and copper tubing at least 1/16" thick (do not use cast metals). The end pieces for boiler and jet chamber are 5/16" sheet brass. The water jacket 5 may be 1/32" brass tubing.

"There are two stages in this pump. The first, or jet, stage is in the upper part, and the second, or annular, stage is located just below. The clearance of the first stage jet depends upon the fore vacuum, and should be adjusted to about 1/32". Most oils cool readily, so the heavy-walled copper tube 2 is insulated by a glass tube 10. Tube 2 rests on the bottom of the boiler, and is adjusted by a 1/4" cap screw 1. The jets are shaped in such a way that they will not clog with oil. This has been a serious defect of most oil pumps.

"11 is a pin for removing tube 2. It can be lifted out with a hooked wire.

"9 is soldered to the tube that comes from the boiler, and acts as a guide as well as a jet. The openings in this jet should have approximately the area of the copper tube.

"A 3/4" length of tubing is soldered to 9. This centers the glass insulating tube 10, so that when the copper tube is removed, the insulating tube will remain in place.

"7 is a glass insulating tube to insulate 8.

"The openings marked B serve as passages for the oil vapor to the first stage jet.

"15 is a copper spinning with a 1/2" hole in its center for the copper tube 2 to pass through. This part of the jet should be accurately centered and soldered in place.

"14 is a trap to let the condensed oil pass back to the boiler without letting the air and vapor through. This trap resembles the trap on a sink.

"13 is a 1/8" strip of brass that carries the oil to the wall of the pump.

"16 is the return tube to the boiler.

"Joints marked A, in boiler and connecting tubes, also 8 and 16, are silver soldered or brazed. Other joints may be soft soldered.

"The cover, 6, shown in detail, sets in a seat and is waxed in.

"The detail of 8 shows a section of the top of the boiler, also the tube that connects the boiler with the jet chamber. This piece, also the ends for the boiler, jet chamber and water jacket, should be turned in a lathe.

"5 is the water jacket that surrounds the jet chamber. It has two short lengths of 1/4" pipe. The water intake should be at the bottom, to prevent trapping.

"The boiler is made of telescope tubing slid into the outer casing. All joints in the boiler should be silver soldered and then be turned in a lathe, so that it can be slid into place.

"When you have completed the pump, connect to a Cenco-Hyvac or equivalent. Make as short connections as possible, especially from oil pump to vacuum chamber. Fill boiler about half full of Apiezon oil 'B'. Place cover on pump and seal with wax. Dr. Strong's mixture, as described in 'ATMA' is O.K. Start the fore pump and scout for leaks. If none is present you should have a high enough vacuum in 15 minutes (using a 9" bell) to start the diffusion pump.

"Heat may be applied to the boiler by a bunsen burner or electric plate. Care should be taken not to overheat. You can tell when the pump is too hot by placing your hand on the high vacuum pipe that goes to the bell: this pipe should be just warm about 3" from the pump. In a short time you will notice the discharge rapidly getting lighter (for this pump works rather fast), until it finally goes out with a clean-up voltage of about 10,000 or 12,000 volts. A neon sign transformer may be used. Let the pump run for 10 or 15 minutes longer, to be sure the vacuum is O.K. Then fire your aluminum. When the coat is thick enough, turn the heat off, but do not stop the fore pump until the diffusion pump has cooled enough to let the oil condense. Then shut down the fore pump and open the air valve to the vacuum ~ chamber. The articles in the July and August, 1937, issues of the Scientific American take you through these steps very thoroughly.

"With this set-up I have aluminized in 17 minutes, although I generally allow 30 minutes. The resulting coats are beautiful-far better than any silvering I have ever done.

"List of materials:

12" of 2-1/2" inside diameter brass tubing 1/16" thick or thicker.

9" of 3" inside diameter brass tubing 1/32" thick for water jacket.

12" of 1-1/4" inside diameter brass tubing 1/16'' thick.

1" of 5/8" inside diameter brass tubing 1/32" thick.

About 1-1/2" of 1/4" diameter cold rolled brass for 2nd stage jet.

3-1/2" of 1/4" inside diameter copper tubing.

9'' of 1/2'' outside diameter copper tubing.

1 short piece of copper tubing 1/8" inside diameter for 14.

Enough sheet brass 3/16" thick, for ends of boiler, jet chambers, 17,18,19, 20, and 21.

Enough sheet copper 1/32'' thick to complete first jet.

1 ea. 1/4 by 1" cap-screw.

3" of 1/2'' inside diameter glass tube for 10.

3" of l-3/8" inside diameter glass tube for 7.

"The Apiezon oil can be obtained from the J. G. Biddle Co., Philadelphia, Pa."

THE above description was submitted to Dr. John Strong, who suggested that the reader also see the Review of Scientific Instruments, Vol. 6 (1935), page 66, describing a similar pump, and the same, page 75, describing another approved design. He mentioned that a good up-jet design that is simple to build would soon appear in a book he was writing. He found some minor faults with Evans' pump, just described, but, on the whole, commended his enterprise. This book, "Procedures in Experimental Physics," has subsequently appeared and it contains a 57-page chapter on the technique of high vacuum, with another chapter on evaporating. These cover this subject of aluminizing with more thoroughness than anything thus far made available anywhere, and in a wholly practical manner; in fact, anyone contemplating the construction of an aluminizing apparatus would probably miss more tricks than one if he did not first learn what is in this new book by the leading authority on this work.

IN the September number F. M. Garland of Pittsburgh, told how he made a strain tester for glass, using a lamp in a box, a ground glass screen and polarizing eyeglasses. Just after we inserted that note we espied an advertisement for the kind of equipment which the Polaroid Corporation makes up as a stock product for inspecting glass containers, tubing, tableware, and so on-that is, doing essentially the same thing as Garland-and asked them for a photo This is reproduced in Figure 2, merely to how the professional makes up the same general elements into a stock product. In their reply, the Polaroid people referred to Garland's rig as "ingenious." They also sent a sample of Polaroid Type I for reducing the apparent brightness of the night sky. "The light from city lamps reflected from particles in the air is often so strongly polarized," they state, "that our friends from Harvard tell it is possible to get rid of a great deal of this light by making the observation through Polaroid, rotating the Polaroid till the darkest condition is obtained. This reduces the intensity of the celestial object but it reduces the stray illumination to a very much greater degree and so increases the contrast."

FAVORITE pitch lap mixtures of out- standing professional workers:

Of D. O. Hendrix, Mt. Wilson optical shops: Coal tar pitch, melting point 170, 2 lbs., Mefford Chemical Co., 1026 Santa Fe Ave., Los Angeles, Calif. Pine tar oil (drug store), amount depending on hardness of the pitch start with 2 liquid oz. and increase judiciously toward 4 oz., if needed in order to bring to desired hardness. To these add 1-1/2 oz. beeswax. In addition, the lap is given a thin coating of beeswax, not alone to eliminate sleeks and scratches due to grit but to reduce polishing friction. Prof. John Strong, in his book "Procedures in Laboratory Physics'', mentioned above, includes a 60 page account of Hendrix' methods of working optical surfaces, which will intrigue advanced workers. We amateurs are plainly not so far behind, but there are things we can learn, too.

Of M. H. Brown, optical shops of the California Institute of Technology, for general use, including work on the 200" mirror: Resin, 1000 grams (about 2 1bs.). S. A. E Penn Oil No. 30, 4 oz. paraffin, amount depending on need; start with 75 grams ( about 2-1/2 oz.) and increase judiciously toward 150 grams. Do not paint the paraffin on top.

As the reader will readily understand, so much special work engages the attention of these two men at present, pressing for completion on schedule, that, against their inclinations, they will hardly find it possible to answer inquiries such as persons mentioned in these columns usually receive in considerable numbers.

IN The Journal of the American Ceramic Society, 2525 High Street, Columbus, Ohio, Vol. 20, No. 2, appeared an article entitled "The Scratch-resisting Power of Glass and its Measurement," by James Bailey of the Hamburg, N. Y., firm of Bailey and Sharpe (now the Optical Glass Products, Inc., by the way). The following paragraphs, quoted from this article, throw an interesting sidelight on borosilicate and other glasses, and complement our discussion of glass, begun in this department last month. "If one piece of glass is scratched by drawing across it the corner of another piece, the contact area is small and the unit pressure is comparatively high. When the corner moves rapidly, the work done in overcoming friction easily generates sufficient heat to raise the temperature of the sliding corner above the softening point of the glass the sliding corner, moreover, becomes so highly heated that it produces a streak of light readily visible in the dark.

"This heating effect brings into the scratching process a new factor, namely, the fusibility of the moving point. Thus a piece of quartz glass, though softer than ordinary window glass, will easily produce a long, deeply cracked scratch in a piece of window glass when drawn rapidly across it, because the rubbing corner remains hard at the temperature attained. A glass corner will not scratch the quartz slab under the same conditions because it softens and loses its sharpness almost at once. It is possible, however, to make a deep crack and scratch on the fused quartz with the corner of a piece of window glass by keeping the rubbing velocity at a very low figure, such as one millimeter per second or less. In this connection, all the common abrasives such as sand, corundum, silicon carbide, and emery have very high melting points, while diamond, the hardest of all, is infusible.

"Grinding experiments show that quartz glass and glass containing large amounts of silica and are the most difficult to grind. The ball test shows that these types are really softer than most other glasses. The reason for this is apparent if a fresh scratch made with a diamond is observed under a microscope. The scratch in quartz glass, once made, undergoes almost no change. The initial fractures do not extend nor does any appreciable amount of material fly out of the scratch. The same applies to a considerable extent in the case of high B₂O₃ glasses. With glasses of the conventional window-glass and bottle types, the initial scratch is small, but pieces begin to fly out of the body of the glass along the sides of the scratch almost at once, and this process continues for a period of several minutes, at the end of which time vastly more glass has been loosened than was initially cracked or apparently injured by the scratch. The ability of a material to resist abrasion, as in grinding, is a measure of its work-absorbing power rather than its true hardness."

NOMOGRAPLIS is the name given by their "worker-out," G. W. Gasper, 3245 Woodford Rd., Cincinnati, O., to six 12" blueprint wall charts on each of which a required datum can be found simply by placing a straight-edge through two known values inscribed along a line and then looking for its intersection with a third line; hence the term alinement charts, also applied to them. For example: Given mirror diameter and focal ratio, automatically find accuracy required in parabolization; or given diameter of eyepiece field lens and focal length of objective, find angular field of view; or given mirror diameter and f.l., find parabolization depth. Similar charts are for exit pupil, for diagonals and for compound reflectors. Not merely a lot of arithmetical slavery saved but the designer can swing a straightedge up and down the lines and visually arrive at his optimum condition, also getting more closely acquainted with the whole gamut. For these charts Gasper asks about a quarter of what might be charged; evidently it's a labor of love. He is a member of the Amateur Telescope Makers of Cincinnati.

SOLICITUDE-or something: Professional optical manufacturer who has evidently just heard of amateur telescope making hobby writes that he learns that amateurs in it "attempt to grind and polish their mirror themselves,' and kindly offers to "prepare to produce these mirrors in quantity." A medal will be awarded to the amateur who submits the most suitable reply (on asbestos) to this optical illusion. "Attempt." Grrrrr!

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