Vol. 16, No. 7
INDUSTRIAL A N D ENGINEERING CHEMISTRY
670
could be detected in hydrochloric acid solutions at pH valuee of 5 . 0 4 . e., a t one-tenth the concentration required with high oxygen content. Other experimenters have detected gas evolution in water which was practically neutral in the absence of dissolved oxygen. There is no question, therefore, but what gas can be evolved from solutions of lower acidity when the oxygen content is cut down.
these (OH)- ions are neutralized by mixing with the main solution. A decrease in oxygen content will cut down the rate of corrosion and the consequent formation of (OH)ions, and will therefore make it easier to neutralize the surface alkalinity. We should predict, then, that hydrogen gas would be evolved with increasing readiness as the amount of oxygen reaction decreases. In this connection it will be noted from Fig. 2 that the critical H concentration for gas evolution at 40' C. is less than it is a t 20" C. This is due, a t least in part, to the fact that the solutions at 40" C. contained less oxygen than those at 20' C. This is a very important point in the corrosion of hot water systems where the absence of dissolved oxygen permits some hydrogen gas evolution. The corrosion rate in the acid region, as determined by the oxygen drop method, shows a rapid increase over that obtained with natural water. The actual total corrosion is really greater than these data indicate, since that part of the hydrogen which is removed as hydrogen gas is not included in the calculations. The reasons for increased oxygen depolarization in acids are undoubtedly that the evolution of hydrogen gas causes turbulence a t the metal surface and thereby increases the rate of oxygen diffusion, and also that the surface film has been neutralized and dissolved. +
ACKNOWLEDGMENT This fact is readily explainable in the light of our theory. The surface film of liquid is maintained alkaline a t a pH of 9.5 only because the rate of formation of (OH)- ions from the initial corrosion reaction is greater than the rate a t which
Much of the experimental work in this paper was carried out under a fellowship from the National Tube Company, directed by F. N. Speller. The authors wish to acknowledge the valuable assistance and cotiperation afforded by this arrangement.
United States Patents on Bone Black and Decolorizing Carbons' By W.D.Horne 175 PARK AvE., Y O N K E R SN. , Y.
HE very general interest in decolorizing carbons that has
T
developed in recent years makes any fundamental information on the subject a matter of importance. The gradual improvement with regard to their composition, means of preparation, methods of revivification, and technic of operation has made them more and more of value. All these later carbons have naturally been compared with bone black, itself a decolorizing carbon supported upon a framework of calcium phosphate and introduced into use in sugar refining by Derosne in 1812. The later-developed carbons will inevitably have much in common with their century-old predecessor and the history of its evolution must logically be a part of any comprehensive consideration of their development. The literature of bone black is surprisingly spare, while that of the decolorizing carbons is much more highly developed. A very good resum6 of the whole subject may be had, however, by reference to the files of the United States Patent Office on the subject, and it is with this in view t h a t the present compilation has been prepared. The subjoined lists present with comparative fulness the United States patents relating to bone black and decolorizing carbons, arranged under various more specific headings and according to their serial numbers. A full index, probably to be published later, has also been prepared, giving serial number, date, patentee, and title, together with the first claim in full of each patent, so that a quick means is afforded of ascertaining the general character of an invention, while further details can be seen by reference to the patent itself. U. S. PATENTS O N B O N EBLACKA N D DECOLORIZING CARBONS , Black pigment: 148,775 Bone black composition: 122,526 Bone black driers: 329,324; 336,137; 335,586; 341,497; 343,666; 749,723; 769,421; 871,705; 984,931; 1,058,369 Bone black manufacture: 153,741; 155,919; 165,344; 178,315 Charcoal furnace; 12,602 1
Presented before the Division of Sugar Chemistry a t the 67th Meeting
of the American Chemical Society, Washington, D. C., April 21 t o 26, 1924.
Chemically treating bone black: 831,805; 1,177,725 Collecting ammonia from char: 287,570; 297,948 Cooling bone black: 61,851; 68,915; 77,935; 93,208; 101,019; 186,327; 199,118; 278,356 Decarbonizing bone black: 530,632; 585,658; 586,278; 592,547; 1,184,397 Decolorizingcarbons: 739,104; 1,133,049; 1,135,216; 1,151,553; 1,195,720; 1,200,713; 1,219,438; 1,249,041; 1,250,228; 1,251,546; 1,262,770; 1,286,187; 1,287,592; 1,290,002; 1,308,526; 1,314,204; 1,358,162; 1,359,094; 1,362,064; 1,368,957; 1,383,756; 1,385,826; 1,396,773; 1,402,007; 1,413,446; 1,438,113; 1,440,194 Discharging devices: 254,474; 257,114; 268,951; 335,586; 351,929 Filter discharges: 329,305; 335,602; 335,603 Furnaces and kilns: 35,212; 85,700; 88,701; 58,702; 89,492; 173,989; 178,286; 221,725; 236,458; 265,876; 303,375; 303,379; 308,476; 314,866; 316,610; 320,110; 337,411; 345,324; 345,968; 407,912; 407,976; 412,781; 414,608; 523,248; 556,603; 557,498; 584,071; 612,319: 624,510; 638,177; 708,898; 796,303; 940,520; 972,023; 978,625; 1,004,176; 1,160,687 Oxidizing charcoal or char: 429,682; 526,180; 538,025; 617,080 Recarbonizing bone black: 509,460; 530,632 Refining substances: 1,435,972; 1,442,372; 1,447,452; 1,448,846 Retorts: 587,057; 644,507; 796,304; 851,409; 912,644 Revivifying bone black: 22,734; 26,457; 27,462; 32,679; 35,160; 36,230; 39,637; 39,638; 40,371; 47,308; 53,534; 54,771; 60,492; 62,537; 62,927; 65,359; 65,457; 65,597; 68,915; 77,935, 93,668; 96,899; 113,279; 114,780; 134,686; 150,521; 161,253; 165,992; 167,235; 178,256; 179,579; 188,006; 188,029; 190,676; 235,942; 249,004; 260,486; 265,723; 279,335; 293,430; 350,170; 450,209; 1,189,896; 1,184,398; 1,207,178 Revivifying decolorizing carbon: 1,074,337; 1,189,896; 1,269,050; 1,326,159; 1,327,222; 1,423 Steaming bone black ,962; 320,110; 391,335; 447,313; 526,180; 947,503 Sugar and bone black filters and filtration: 13,740; 329,184; 329,185; 329,210; 329,306; 329,329; 329,330; 329,332; 335,622; 335,763; 340,005; 961,180; 1,430,200 Washing bone black: 263,710; 360,581; 529,469
