INDUSTRIAL i l S D EA-GILVEERI.$'G CHEMISTRY
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This difference in volatility is in the same direction as the difference in carbon formation in the coaches for the two oils and perhaps of the same order of magnitude. The three factors listed earlier in the discussion as influencing the carbon residue test almost undoubtedly are those most important in determining carbon-depositing tendency in an engine, but they cannot be sorted out and evaluated from the single figure of the Conradson test, any more than the values of three unknown quantities can be determined from one equation. Factor (a), the asphaltic material in the oil, while having a large influence on the carbon residue test, might change the engine carbon deposit very little. A logical deduction from this would suggest heavy clay filtering of an oil before applying the carbon residue test. The authors have tried this, but have no conclusive results yet. Factors (b) and (c), the proportion of non-volatile residue and the proportion of coke left by this residue on cracking, may conceivably vary independently; but it is the authors' experience that an oil which leaves very little residue non-volatile a t flame temperatures also leaves very little of this residue as carbon. Such conduct seems to be an inherent property of naphthenic oils. It should be remembered that only volatility a t combustion chamber temperatures is important since good oils are not volatile a t piston wall temperatures. A fourth factor in engine carbon deposits, which is not reflected in the carbon residue test, is the character of the coke formed on cracking. A dry, powdery form, free of binder, is desirable, since mechanical influence inside the engine can easily remove it. This is brought out forcibly by the-present work with sleeve-valve engines. such loose deposits Seem also to be an inherent characteristic of naphthenic oils. Conclusions
Such conclusions as may be drawn, while tentative, are clear. The carbon residue test is a fairly reliable index of
Vol. 21, No. 10
due test. Its success is most conspicuous in evaluating paraffinic oils. The setting, in oil specifications, of reasonable upper limits for carbon residue values in the same viscosity class should protect the user from excessive carbon deposits, because a paraffinic oil of low carbon residue value must be very highly refined; a naphthenic oil, always of low carbon residue value, has an inherent tendency to low carbon deposit. In either case the user will be protecting himself against abnormal carbon deposition. For sleeve-valve engines the situation seems to be different. A paraffinic oil of very low carbon residue value was only slightly better as to carbon deposits than one of normal carbon residue value, and both were very strikingly inferior to a naphthenic oil. The characterizing of such a naphthenic oil seems possible best by a vacuum distillation specification. A tentative recommendation might be that such oils, in addition to being otherwise suitable, should show a t least 90 per cent volatility distilled under 10 mm. pressure in a test similar to that described above and should boil between suitable limits of liquid temperature, these to be set for the particular equipment in mind. For the coach engines used in this work these limits might be between approximately 550" and 700" F. (at 10 mni. pressure). Probably 5 per cent could be allowed t o distil over below the lower temperature limit. Other suitable upper and lower limits must perhaps be set for other types of sleeve-valve engines. Acknowledgment
The authors wish to acknowledge their indebtedness to
H. C. Mougey, chief chemist of the General Motors Research Laboratory, who has been connected with this work since its inception, and from whom the authors have received both inspiration and assistance. Literature Cited
Effect on Concrete of Acid Water from Stored Bituminous Coal' Edgar F. Wolf C
(1) Atwmd nnd Johnson. Tionr. A m . Soc. Ciail E n g , 81, 204 (1924) (2) Hayiis, Proc. Am. SOC.Civil En#.,68, 549 (1926). Coal Ass. 86, 557 (19'24). ( 3 ) BTOMD;, (4) Enon, P l O C . En#. SOC. wmi. Penno.. 88, 309 (1923). (51 Prost, BaloiiimwcBn#., s, 11 (1928). (0) 15eire. Conirels, 18, 249 (1921). (7) Sclvig and Rateliff, J. INO. ENC.Cwar., 14, 126 (192%); Starilfird Methods ioi Iiraniieation of Water and S w w e . Am. Pubiic Hcrlth Asrocn., 1825, p. 35. (8) Tuttie, Mmi&W Bag. 1..7, 80 (18?1). (9) Wip nud P c i s ~ m nEn#. , Nerils-Rciord, 19. 532. G43,889. 737.794 (1917). 1101 Concrrls. 19. 53 (1921).
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