WILLIAM S. HILL tl'fember, Examining CQrps, United States Patent Office Formation of Thin Films upon Glass Surfaces. No. 2,337,460. Preston W. French, Wilkinsburg, Pennsylvania, assignor to Pittsburgh Plate Glass Company. Since the pioneer work of Langmuir, Blodgett, Strong, Cartwright, and others, a great deal of development has taken place in producing reflection-reducing films on lenses and viewing elements of optical instruments. One general method has been to superpose on the glass a film of organic material having a thickness of about one-quarter of the wave length of visible light and having an index of refraction such that the reflection at the interface of air and film equals the reflection at the interface of film and glass surface. The patent describes the formation of a film of increased strength, the film being composed of calcium fluoride. The surface of the glass may first be etched with 1 or 2 N strong mineral acid containing in solution some of the calcium salt of the acid. The treatment is stopped when a substantial amount of the alkali component of the glass has been leached out to a depth of about 12 millionths of an inch. The glass is then removed from the acid bath, \vashed, dried, and treated with hydrogen fluoride mixed with air or inert gas. This converts the silica in the surface film to silicon tetrafluoride which is volatilized. What is left is a skeletal film of calcium fluoride. This film is baked at about 200°C. for 10 minutes to harden. Process of Making Filaments Consisting of Pure Silicic Acid. No. 2,338,463. Franz Skaupy and Gustav Weissenberg, vested in the Alien Property Custodian. This invention is a novel and interesting method of making filaments of pure silicic acid, more particularly quartz, which has seemingly excellent possibilities. The old method of making these filaments is to spin fused quartz at extremely high temperatures. It must be remembered that quartz melts at 17lO°C. This patent describes both a wet- and a dry-spinning method of low temperature filament manufacture, of which the dry method is preferred. An example of the wet method is to prepare a filtered and deaerated 1:5 solution of commercial potassium water glass in water. Tbis is then spun into a 5 per cent solution of hydrochloric acid which coagulates the silicic acid. After being wound by spinning centrifuges, the filament cake is treated with dilute acid to remove . the soluble chlorides. One example of the dry-spinning method is to take commercial double water glass, having the composition ] N a 20, ] K 2 0, 6Si02 , and form a solution having a
[76
specific gravity of 60° Baume. Very fine filaments ar, dry spun and then treated with 30 per cent nitric acid The filaments are finally run rapidly through a g flame or other heating zone to vitrify the silicic acid. I A third modification may also be used in which fusei commercial water glass is spun into a stream of co~ pressed air. Even this results in great economy of heal since the required temperature is below 1000°C. An interesting sidelight on the different results ob: tained by using the various modifications of the meth~ is that the microcrystallites of the wet-spun filamenti are probably oriented to a great extent parallel to t filament axis. Stretch-spinning also increases orientaj tion. This type of filament is more extensible than tht unoriented type. Manufacture of Sulfuric Acid. No. 2,337,060. Lewis S. Munson, et at., assignors to E. 1. du Pont dt Nemours and Company. This is an improvement in the well-known contact process of manufacturing sulfuric acid. The invention relates to that modification of the contact system in which the burner gas is passed directly to a platinum-type converter without intervening scrubbing or other wet purification. Ordinarily the presence of too much moisture in the air, undesirable chlorine in either air or sulfur, and the general presence of dust, all contribute to lower the efficiency of the abbreviated contact system. The patent describes the removal of moisture from the burner air by means of a drying tower containing concentrated chlorine-free sulfuric acid. The chlorine is removed from the sulfur by melting and being allowed to stand until the chlorine, along with fine mineral matter and asphalt, settles as a sludge. Dust is reo moved from the burner air by a coke filter. Production of Sulfathiazole. No. 2,339,083. L. C. Leitch, Montreal, Quebec, and L. Brickman, Quebec, Canada, assignors to Mallinckrodt, Ltd. This is an improved method of preparing one of our highly important drugs. Sparingly soluble salts of certain sulfonic acids are coupled, in the presence of a tertiary amine such as pyridine, with a derivative of a benzenesulfonyl halide having in the para position one of the following: N02 , a halogen, an azo group, or -NHR, where R is an acyl group. A more specific example of the method follows: To a hot solution of 25 g. of sodium 2-chloro-p-cymene-3· (or -5-)sulfonate dissolved in 200 ce. of water were added 50 cC. of aminothiazole hydrobromide liquor. The solution was boiled with carbon black and filtered,
177
APRIL, 1944
and the salt crystallized from the filtrate. The crystals were then washed in cold water and dried. They may be purified by recrystallization. The yield was 24-5 g. To the crude salt mixed with 50 cc. of pyridine there were gradually added 12 g. of p-acetaminobenzene sulfonyl cWoride, and the mixture was heated at 95°C. for two hours. The solvent was removed in vacuo and the acetyl sulfathiazole isolated by adding 200 cc. of water and filtering off the solid. The yield was 9.8 g., melting at 248°C. The acetyl sulfathiazole (or other derivative as the ,ase may be) may be hydrolyzed to sulfathiazole by any of the standard procedures with aqueous alkalies or mineral acids. The improvement lies in using the aminothiazole salts, since this avoids having to isolate aminothiazole from a reaction mixture. The present method also supposedly produces a higher yield and the precipitants may be recovered from the mother liquor after the salt is coupled with the sulfonic acid. Preparation of Malonic Esters. No. 2,337,858. W. C. Stoesser, Midland, Michigan, assignor to Dow Chemical Company. The invention relates to the preparation of the lower alkyl esters of malonic acid by the simultaneous hydrolysis and esterification of sodium cyanoacetate. The reaction representing this well-known process may be represented by the following equation: CN
COOCzH~
I I 2CH z + 4C2H~OH + 2H zS04- + 2CH I I COONa
2
+ Na S04 + Z
COOC 2 H b (NH.)2S0.
The improvement resides in recovering the appreciable amounts of the mono-alkyl malonate and free malonic acid formed during the hydrolysis and esterification. By returning these to the reaction a considerable increase in yield is obtained. Process of Preparing an N-Acetyl Aromatic Amine. No. 2,337,825. George G. Lahr and W. T. Daddow, Wilmington, Delaware, assignors to E. 1. du Pont de Nemours and Company. The preferred method is described as follows: Eighty-eight parts (0.86 mole) of acetic anhydride are added little by little to 160.5 parts (1.5 moles) of p-toluidine, allowing the temperature to rise. The mixture is heated to reflux temperature after all the anhydride has been added and held there (150° to 160°C.) for one and one-half to one and three-quarters hours. Vacuum is applied and dilute acetic acid is distilled ofe the vacuum being raised as the temperature drops. The bulk of the acetic acid distills during crystallization of the mass, which occurs at 115° to 125°C. and a
vacuum of 2:2 to 26 inches of mercury. After removal of the weak acetic acid, the vacuum is released and 25.5 g. (0.25 mole) of acetic anhydride are added to the charge and heated at 150° to 160°C. for a half hour. Acetylation is about 99 to 100 per cent complete. Method and Apparatus for Quantitative Analysis of Radioactive Substances. No. 2,337,306. R. B. Barnes, Stamford, Connecticut, assignor to American Cyanamid Co. This is an interesting method of determining the total quantity of an element present in the form of its radioactive and nonradioactive isotopes. In naturally radioactive elements such as potassium and rubidium the radioactive isotopes are invariably present as a known proportion of the total quantity of the element being determined. In the case of potassium it is known that a radioactive isotope of potassium, designated K40, is present naturally in the ratio of 0.012 per cent with ordinary potassium. A conventional Geiger-MUller counter may be used to measure the radioactivity. The solution of unknown normality is placed so that the rays of particles from the radioactive substance pass through the shell of the Geiger tube. These rays or particles, together with the voltage impressed on the tube, ionize the contained gas, thereby causing a current to flow through the external circuit used to impress the voltage on the tube. This current is amplified and used to trip a relay counter, thus recording the particle causing the ionization of the gas and thereby giving a statistical measure of the amount of the radioactive isotope present which originally caused the ionization of the gases. The count for a period of two hours or so is taken and the net count per minute determined. This is compared with a graph made of counts taken with solutions of known normality. The normality of the unknown can then be determined with reasonable accuracy. Absolute accuracy can be obtained only by measuring the radioactivity over a long interval. In case the radioactive isotope has a short half-life the decay is described by the following equation for radioactive disintegration:
where N, is the number of atoms of the radioactive element after a time interval t • No is the number of atoms when t = 0 X is a constant for the disintegration of the particular element being analyzed.
The method is said to be applicable to elements such as radioactive iron, sulfur, sodium, calcium, cobalt, zinc, carbon, chromium, manganese, and many others.
One hundred average householtl till c(~ns wei.gh 100 pou.nds and yiebJ 1.2 pOluuls oj lin, by recovery.
