690 U . S . BUREAU OF CHEMISTRY NOTES. [J. F. I.

this condition is not altered by boiling with water at ordinary pressure or by cooking under a steam pressure of fifteen pounds; and (2) that the nutritional failure of arachin is due to the retention of a considerable part of one or more of the essential animo acids, the most conspicuous of which is histidine, in the indigestible complex. The total amino acid composition of arachin would almost certainly be quite adequate, if it were available.

A direct comparison of the digestibility in vitro of arachin with that of casein and of cooked phaseolin gave the following (average) values for percentage of digested nitrogen, calculated on the basis of the total amino, minus free amino nitrogen: Arachin, 48.5; casein, 61.4; cooked phaseolin, 58.7 . The control proteins are known to be sufficiently digestible to be available. An extremely indigestible partial cleavage product, produced by warming arachin with o.I N sodium hydroxid for two hours and precipitating the unattaeked residue with very dilute acid, contained somewhat more than two-thirds of the total histidine, and about two-fifths of the total lysine of the arachin from which it was derived.

The experiments indicate that the incomplete digestibility of arachin is not due to changes brought about by the treatment involved in its isolation, but is a native property of the protein. The high nutritional efficiency of peanut meal is therefore to be attributed to the presence in the meal of sources of amino acids which supply essentials contained in an unavailable form in arachin.

T H E P L A G I O C L A S E F E L D S P A R S AS A C A S E O F ATOMIC I S O M O R P H I S M . s

By Edgar T. Wherry.

[ABST~Cr.I

THE structural formula viewpoint is incapable of accounting for the isomorphism of the plagioclases, the arithmetical view- point mistakes a corollary for a cause, and only the atomic iso- morphism viewpoint really corresponds to the data. As sodium is indicated by X-ray measurement to occupy approximately the same volume as calcium, and aluminium as silicon, the two feld-

' Published in Am. Mineralogist, 7, July, I922, Ix3.

Nov., i922. ] W . S . BUREAU OF CHEMISTRY NOTES. 69I

spars may well have identical geometrical s t ructures; the valence relations in solution merely require the one replacement to be accompanied by the other, and do not persist into the solid fo rm of the compounds. Orthoclase and carnegieite can not be isomor- phous with anorthi te because the potassium atom of the one, and still more the two sodium atoms of the other, demand more space than displacement of the calcium can furnish. The simplest for- mulas adapted to br ing out all the relations are : Albite, NaAI- (S i308) ; anorthi te CaAl(A1Si2Os) .

Additions to Research Staff of the Eastman Kodak Com- pany.raThe following experts have recently been added to the lab- oratory of this company: Dr. Helge Schibsted, formerly with the Atmospheric Nitrogen Company; Clyde Brockett and D. H. Harris, Massachusetts Institute of Technology, 1922 ; A. Burgess, Bates College, 1922 ; R. P. Loveland, Grinnell College, 1922. H . L .

The lq'requency-Sensitivity of Normal Ears. H. FLETCHER and R. L. WEGEL. (Phys. Rev., June, I922) . - -The sensitivity of the ear is here given in terms of the alternating (root mean square) pressure requisite for the production of a minimum audible sensation. " A tone of IOOO cycles per second requires only one-sixtieth as much pressure variation for audition as. a tone at IOO cycles per second. The aver- age sensitivity for normal ears varies f rom. 15 dyne at 60 cycles to .ooi dyne at IOOO cycles. Between IOOO and 4000 cycles the sensitivity is approximately constant and equal to .ooi dyne per square cm."

An inspection of the curves connecting pitch and sensitivity in terms of pressure leads to the thought that individual differences are as sharply characteristic as they are in thumb prints. For instance, one person manifested a remarkable drop in sensitivity at 3000 cycles, and this held for both ears, though until 4500 cycles was reached the left ear exceeded its fellow in sensitivity. For the rang~e of fre- quencies used in speech the following relations are stated : " Persons who have normal hearing require approximately .ooi dyne per square centimetre in order to hear sounds in this range. Persons who require pressure variation of .I dyne per square centimetre are called slightly deaf. Those who require one dyne are partially deaf but can usually follow ordinary conversation. Those who require IO dynes belong to that class who use ear trumpets or deaf sets to amplify the speech waves. A pressure variation of approximately IOOO dynes can be felt and produces a sensation of pain.

" This shows that among people who can follow ordinary conver- sation there is a range in ear sensitivity of more'than IOOO and among people who are noticeably deaf there is another range of IOOO, making a total range of more than a million for people who can hear or be made to hear by means of amplifying devices." G . F . S .