Peter L. Martin, lens maker, of 829 East Thayer Street, Philadelphia, writes: "One day Doctor Brashear told me to empty a vessel containing the residue of silver solutions that had been standing (Italics ours.-Ed.) and remarked that it had the danger of dynamite. Another time I was polishing within four feet of him when he was silvering a large mirror and as he poured the solution on the mirror the liquid went up in the air and some fell on the back of my shirt.

"Every Saturday morning the professional optical worker, Mr. Octavie Petitdidier of Chicago, silvered, using the Brashear method, and it never exploded and we never mentioned goggles. Dates 1907, 1908, 1911, 1914.

"About 1921, I gave a silverer the modified solution mentioned in Ritchey's book. When I asked him how it worked, he said, 'Say, that stuff exploded.'

"I think the suggestion about wearing goggles is very good. The solutions have never exploded on me, but during the few minutes that it takes the amateur to pour on the liquid it is well worth while to take every precaution. I intend to wear goggles in future.

"I have heard of several other explosions of the silver solution. In one instance an employee, in order to see better, pulled up the window shade and the solution which had been standing all night (Italics ours.- Ed.) blew up, when the daylight struck it. Another time a worker was badly hurt and laid up for several weeks.

"My conclusion is that the original Brashear solution as given to the world by John A. Brashear is not likely to explode."

NEXT we get testimony from K. L. McAlpine, 223 B. Sansom Street, Upper Darby, Pennsylvania, who writes: "Although I have used this process a great many times, on one occasion only have I met with an accident. In June of last year, having finished silvering a mirror, I placed the remainder of the silvering solution in a cold room in the laboratory. This room is maintained a few degrees above zero. This solution contained silver nitrate, ammonia, and soda only, as none of the reducing solution had been added to it. In view of the temperature and the absence of organic matter in the solution I considered it to be quite safe. In August the solution was removed to the basement and remained there for about one month. (Italics ours.-Ed.) The bottle was moved about many times during this interval.

"The explosion took place one night, fortunately when no one was at the time in the building. Although there could not have been more than 50 cc of solution, practically every piece of glassware in the room was broken. Even a nine liter Pyrex bottle was shattered, and the white walls and ceiling were sprayed with the brown-black silvering compound.

"While the Circular-Letter on silvering prepared by the Bureau of Standards very -plainly states that the silvering solution should be made up just before use, I believe that still more emphasis should be laid on this point, because otherwise I am quite sure that many, in anticipation of trouble with the silvering, will make up a stock solution."

IN Pasadena, at 88 North Delacy Avenue, is the firm of Howell and Sherburne, designers and builders of special machinery and scientific instruments, including the Hale spectrohelioscope. Waldo E. Howell, son of the senior member of this firm, writes as follows: "I am very glad to tell you about two explosions which happened recently and were by no means mild. To give you a better idea as to the danger of this kind of explosion, I am enclosing a photograph of one end of our optical shop.

The shelf marked 'X' with the arrow is the spot where the bottle of solution was at the time it exploded. This shelf was blown completely off the wall. The amount of solution in the bottle, which was not confined, was 16 ounces of silver solution ready to be mixed with reducing solution for silvering. Pieces of the bottle in which the solution was contained were no larger than fine shot, when we swept the floor. Small pieces of glass were buried in the shelf. I do not think the explosions would have occurred had the temperature been lower. It was about 85 degrees when I finished silvering, and this silver was left over. (Italics ours.-Ed.) It exploded of its own accord in solution. Fortunately, no one was standing next to it.

"When I tell you of the second explosion I believe you will decide, as I have, that after the caustic solution is poured into the cleared-up silver nitrate solution, an explosion may occur at any time. This explosion happened in the middle of the process. I guess, before I go on, I had better stress the fact that in both cases directions had not been followed to the letter as to temperature, (Our italics.-Ed.) but I silver many times in the summer at 85 and even up to 100 degrees, and I really have no trouble, either with solutions or with soft coats of silver. However, in this case the temperature was nearly right, but I believe the difficulty came in after the silver nitrate solution had been cleared with ammonia. The caustic solution, having been poured into the silver nitrate solution, was not stirred and ammonia was not added for about ten minutes. When my friend, Mr. Seigel, did get back to the solution, after the ten minutes and started to stir and add ammonia, the explosion took place.

"Everything would have been all right, had he gone right on as the directions say, but the interval between the clearing up of the silver nitrate solution and the pouring in of the caustic solution was too long, thus allowing the explosive silver fulminate to gather on top of the solution. Just as he started to take hold of the glass rod and stir, there was a terrific explosion. The 2-ounce beaker, which was of heavy glass, was never found in any pieces larger than BB shot. The fragments were lodged in the wall, below the surface. Mr. Seigel nearly lost his sight from the flying solution. He was in bed for a week, and later had to wear glasses. It probably seems funny that the solution will explode in water, but this it did.

"I still use the same method, but I watch very carefully to see that no undue amount of fulminate is allowed to form on the surface of the solutions when I pour the caustic solution into the silver nitrate solution. If this fulminate does form in visible amounts when I pour the caustic into the silver, I quickly pour in ammonia. However, this will be unnecessary, even on a warm day, if ice is used."

FINALLY, part of a communication from Dr. John Albert Marshall of San Francisco, is quoted from the Journal of the American Medical Association. In certain kinds of work they do, Iaboratory biologists use essentially the same process as is used by the telescope maker:

"An explosion occurred Tuesday, March 11, which has jeopardized the eyesight of a research worker in one of the laboratories at the University of California. Sections of bone and teeth with their contained soft tissues had been stained by the so-called silver nitrate method. The dishes containing the ammoniacal silver oxide solution were inadvertently left standing in the sun from Saturday noon until Tuesday morning. There were traces of alcohol in the silver solutions carried there by the sections of tissue. The sunlight hastened a chemical reaction between the silver, the ammonia, and the alcohol, and there resulted from it a highly explosive, very sensitive and unstable compound, silver fulminate-to be distinguished from the so-called fulminating silver, which explodes on drying.

"When the dish was taken up to be emptied and cleaned, it was warm from the sun. The mere movement of the liquid was responsible for the detonation.

"Since the accident was so serious to one of the workers and endangered others in the laboratory as well, a word of caution as to the handling of these silver solutions is necessary."

WHAT, then, are the indications from all this evidence? Half a dozen explosions out of thousands of silvering jobs, and most of these due to carelessness. There is little reason to fear the job, but one ought to respect it by wearing goggles. Nature will usually patch up a complexion peppered with glass fragments but an eye is an eye.

Judging from the comments quoted above, the explosions are seldom of the full power of a typical dynamite explosion, and some of them are probably comparatively feeble. But no one craves an invitation to be present even at the time of a feeble explosion.

Here is another expedient tip-don't let the ladies at home see these pages.

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