134 CURRENT TOPICS. [J. F. I.

tetany and its convulsions are attributed to the decreased mag- nesium content of the blood serum.

J. S. H.

Freezing Point of Hen's Egg.--H. P. HALE (Proc. Royal Sot., London, 1933,/3, CXII, 473-479) states that the freezing point of the yolk of the hen's egg may be taken as - 0.57 ° C., and the freezing point of the white as - 0.420 C. When seeded separately, both the thick white and the thin white have the same freezing point, -0 .420 C. ARTHUR W. THOMAS AND M. IRENE BAILEY (Ind. Eng. Chem., Ind. Ed., 1933, XXV, 674) report that the freezing point of whole-egg magma ranged from -0 .462 ° to - 0.47 °0 C.

J. S. H.

Oak Forests of Pennsylvania.--According to A. C. MCINTYRE (Pennsylvania State College, School of Agric. and Exp. Sta., Bull. 283, 1933, 28 pages), " the oak forests of Pennsylvania are mainly of sprout origin, the product of cutting the virgin stands and the recutting of the second-growth. Many stands have been cut over three or four times, their regeneration being principally from sprouts." They contain 9 species of oak (white, chestnut, red, scarlet, black, pin, scrub, scrub chestnut, and swamp), of which the first 5 species predominate. These forests also contain at least 50 other species of trees. Under average conditions, the forests are growing at the rate of 0.6 cord per acre per annum. Growth of I cord per acre yearly occurs only on the better sites, such as moist fertile benches and coves. The forests are thrifty where fire has been kept out; probably less than 25 per cent. are normally stocked, but normality is approached with increasing age. They form an important economic resource of the state.

J. S. H.

Gelation of Frozen Egg Magma.--In the food industries, eggs are removed from the shell, mixed by churning, and cold stored hard frozen at a temperature of - 18 ° to - 2I ° C. When the frozen mass is thawed after storage for at least a few weeks, it usually is quite thick in consistency. ARTHUR W. THOMAS AND M. IRENE BAILEY (Ind. Eng. Chem., Ind. Ed., 1933, XXV, 669-674) find that the degree of gelation of thawed whole-egg magma is governed by the mechanical treatment of the magma prior to freezing; the greater the disruption of the magma during churning, the lower is the resulting degree of gelation ; colloid-milled specimens show practically no gelation. The degree of gelation becomes

July, I933.] CURRENT TOPICS. 135

greater the higher the per cent. of total solids or of ether extract (crude fat) in the magma. The degree of gelation is decreased by the addition of sodium chloride, dextrose, or sucrose to the magma; equimolecular quantities of glucose (dextrose) and sucrose produce the same effect; masses of sodium chloride (salt} and sucrose, which give rise to the same depression of the freezing point, apparently have the same effect on gelation. The degree of gelation is not governed by either the total phosphorus or the lipoid phosphorus content of the magma. The maximum gelation is attained during storage for 60 to 120 days.

J. S. H.

Vitamins of Tuna MeaL--ROGER W. TRUESDAIL AND LEE SHAHINIAN (Ind. Eng. Chem., Ind. Ed., 1933, XKV, 661-662) have made biological assays of fresh, vacuum-dried meal prepared from the meat of the tuna fish (Neothunnus macropterus), chiefly the dark meat. The sample contained: Protein 62.09 per cent., ash 18.24 per cent., moisture 8.61 per cent., fat 8.04 per cent., crude fiber o.5o per cent., free fat ty acids 0.97 per cent. The meal was a good source of vitamin fat-soluble A, containing more than 14 units per gram, and an excellent source of vitamin fat-soluble D, containing more than 62 units per gram. These results suggest that the white meat of the tuna, which is canned and used as a food for man, may be a source of these vitamins in the human dietary.

J. S. H.

Toxic Gaseous Products of Combustion.--JOHN C. OLSEN, GEORGE E. FERGUSON, AND LEOPOLD SCHEFLAN (Ind. Eng. Chem., Ind. Ed., I933, XV, 599-6o3) have determined the gaseous products obtained when certain substances are decomposed by heat in the absence of oxygen, and when these substances are burned in the presence of an excess of air. The substances were cellulose (news- papers and wood), oils (gasoline), rubber insulation, wool, and silk. The gaseous products varied both qualitatively and quanti- tatively with the substance and the mode of heating, and included carbon monoxide, carbon dioxide, hydrogen, acetic acid, methane and other saturated hydrocarbons, unsaturated hydrocarbons, oxygen, nitrogen, hydrogen sulphide, sulphur dioxide, ammonia, and hydrocyanic acid. Silk and wool were sources of ammonia and hydrocyanic acid, and wool also yielded hydrogen sulphide and sulphur dioxide. Of the textiles, cotton and rayon gave rise to the least toxic gases, silk and especially wool to the most toxic gases. Inspiration of air containing more than 2 or 3 per cent. of carbon dioxide increases the respiratory rate. However, inspiration