There's value in numbers... ιLETTERS

'u.s.PAT. 1,601,193 I u . s .PAT. 2,271,882 I u.s.PAT. 3,o Photochromism vs. U.S.PAT. 1,601,506 U .S .PAT. ,2,273,313 U .S .PAT. 3,o phototropism U.S.PAT. 1,601,507 ·. VïS&kiï' 2» &'73,827 U.S.PAT, 3,0 DEAR SIR: V. S.-PAT. •:•·· 1 y.676 , 7 2 7 · U. S. ~°'>m- 0 r ° 7 ^ ^ - f f f f | f [ i ° P,Atn 3 , 0 Color changes brought about in ma­i l . Ρ τ " · " Ί " I "· ι ι ι " ; ' Τ Τ | , ' · ' · ' : Ί Ί ' ι ΐ I i l 3.*fl t e î i a I ? b y l n c i ^ e n t l i g h t a n , d * 5 e ? v e r ~ TT Q χ,ΛΓπ ι η ι il'1 "* ττ ο U A I ^ ^ V V R sal of such changes in the dark are

I | III ' " ' I I 2 , ^ 7 5 , 0 4 9 U . b . P A j 3:,Q phenomena that occupy an interesting m&jU\ I . ' " I . S8 U . S . P A T . 2 , 2 7 5 , 4 2 2 U . S . P A T l - ' 3 , O and important area of the field of ;tïÎ|)fPA.T. 1 , 6 9 3 , 0 1 5 U . S . P A T . 2 , 2 7 6 , 3 1 4 4 J * M # - T 1 3 , 1 photochemistry. The phenomena are =UJ3.PAT. 1 , 6 9 4 , 1 5 5 υ . 3 . Ρ Α Τ . ^ ^ | ί ^ 7 β Ι Τ ΐ 7 » Α τ 1 3 , 1 often dramatic and the mechanisms in-IIJfc PAT 1 6Q8 λ^Ι . L K ; ^kimm^Wà^A^Êm « Α Φ Ι Λ Ι volved are complex and, as yet, not \ ¥ \ ptm* ί ' ^ Λ ρ η • « ' » M ô M ^ l l ^ ' ^ ' I v i l ^ T ' well understood. But the literature on .U..1. J J J » . « L , q ^ ^ p o 0 β ^ · Η ^ · ^ 1 2 ! ^ ^ ^ ΤΤ. υ . Ρ Α Τ . Ι , ^ Ι . . this subject is further and unnecessa-' t t r l . Λ VL , i J K ^ A 3 J ï ^ ~ 2 8 3 , 1 7 2 J U. S. PAT. B ' j l i rily complicated by the use of two dis-U , l P m / · · ^ * U . S . P A T . 2 , 2 i U | - i * W U . S . P A T . W}t tinctly different terms: photochro-U . » P M T 1 , 3 3 7 , 3 8 1 L l J ^ ^ I / l l M A ^ l B t t U . S . P A T . 1 , 1 ' mism and phototropism While study-U S I P AT 1 ^ 7 Λ 1 ^ Μ Γ 3 • £ I S A J T I U I I I q ΡΛΤ VA/ i n g t h e l i t e r a t u r e f o r t h e Preparation ττ ο V ' Ϊ i s l t ' V " W m i / ^ T ' TO o f a r e v i e w a r t i c l e o n Photochromism U.S.1PAT. 1 , ^ 4 1 Μ ί β M S . ^ T . J P | 2 T u f , 2 7 7 U . S . P A T . M in triphenylmethanes (soon to be pub-U . S . f A T . l , 3 4 3 ^ w F flrS.PAT. 2 , 2 8 9 , 9 1 8 U . S . P A T . * & lished in Photochem. Photobiol. [6, U . S . 1 A T . 1 , 3 4 4 , 8 9 1 U . S . P A T . 2 , 6 8 1 , 8 7 5 U . S . P A T ^ ? , » 779-797 (1967)], I became increas-U . S . A l T . 1 , 3 ^ 5 , 3 1 7 U . S . P A T . ι || l l l l ' l l ' F ingly aware of the confusion which the II S ^ P I T 1 T.S1 ΙΛΟ ΤΤ S Μ ι ι ρ, use of these terms affords the reader. e Ê - ' ^ t i ' I ' w ^ J - 5 ,4 Throughout the literature authors ^ ^ ^ V "* " " ^ ι Τ Ή > m " · " ^ ° ^ " ' ? ° η I " " " T "· °' have apparently disagreed about ÎIï S;%klLT' J ^ ' k o . , 3 0 5 /υ;.8ν.ΡΑΤ.--''2^'865;*7θ1-Τϋϊ3νΡΑ']?.ν.'3>2ι which term is best, some using photo-U . S . & T ^ ; # ^ f f V 8 5 7 ' U. S.PAT, 2^ ,865 ,798 , ÎF.SiPiCTl 3 , 2 ' tropism [Chem. Rev., 65, 247 U . S . P A T . 1 , 3 7 3 , 2 2 4 U . S . P A T . : 2 , 8 6 7 , 5 8 7 U . S . P A T . 3 , 3 : ( 1 9 6 4 ) ] a n d s Z e " t g vY°c]?0-

' ' I ι ι is > \ 7 mism (Ααυαη. Photochem., 1, Inter-I science, New York, 1963) to describe

Thousands of patents on new developments involving soluble silicates t n e s a m e phenomena. have been issued in the last lOyears alone. It's a healthy and prosperous t t

T h e , t e r m p h f ° t r o P l s m ( ° ' Ph°-.,, ' totropy) was first, and properly, used

° by biologists to describe the leaning or Patent numbers in such abundance prove that the utility and commer- turning of plant stems and foliage to--cial value of soluble silicates have been realized time and time again in ™ard

nJa s.our^e

7 of h | n / ^ / m i

a hos, of Men,,»,», profitabte products and processes. £ & * £ " £ £ £ £ » } Ξ And you can benefit from this kind of activity! The big PQ line of over applying this term to the phenomenon 70 sodium and potassium silicates offers combinations of unique prop- °f reversible color change caused in erties that could stimulate your research imagination and enhance the substances by incident light. This marketability of your products. m e a n i " § ls

t n o t . e f t î Jn th* p h l l < >

J logical roots as is the biological mean-We've got helpful literature. As a starter, try Bulletin 17-1, "PQ Soluble ing. The better term photochromism Silicates, Properties and Applications." Return the coupon and we'll h a s gradually come into use but it has send you a copy . . . it could help solve a research problem. ™ver replaced phototropism, although

the two nave become more or less synonymous. In contrast, the closely

I 1 related term thermochromism gradu-I ,_, I ally replaced thermotropism many 1 D AppÛcItiorÎs0^ Π 1?'h " P Q S ° I U b l e SHiCateS ' P r °P e r t , e s a n d I years ago and the latter cannot be ! 1—1 r>i 1 x_i J . . I I χ - . ,, ... . . I found in either a recent review of that

• Please keep me posted on current developments in soluble silicates via ι , . r^,7 „ on Gt* , ^ û o n

your monthly publication, "Silicate P's and Q's." subject [Chem. Rev., 53, 55 (195,3) J or recent Chemical Abstracts indexes.

ι Name jj t |e ι I will grant the acceptance of a | ι word through common usage and also, j Company I ^ necessary, the acceptance of two I Address I meanings for the same word. After I I all, confusion of this type exists for I CitV State Zip | thousands of words, e.g., "fast."

S However, the inconsistency in the use

Β PHILADELPHIA QUARTZ COMPANY,1162PUBLICLEDGERBUILDING,PHILA., of *? p T ce ^ J ^

PENNA. 19106 - PHILADELPHIA QUARTZ COMPANY OF CALIFORNIA, JStaLîly Τ te^io? w S l BERKELEY, CALIFORNIA, 94710 • NATIONAL SILICATES LIMITED, ble l ight- induced color changes, are ® TORONTO 14, ONTARIO "SILICATOS y DERIVADOS, S.A., TLALNEPANTLA, exasperating. Therefore, I propose EDO. de MEXICO • SERVING THE NORTH AMERICAN CONTINENT I the fo l lowing:

6 C&EN OCT. 30, 1967

The term phototropism as it is now used should be discarded from chemi­cal literature not only because it is a complete philological misnomer, but also because the use of both terms provides confusion for searchers of abstracts indexes. The more descrip­tive term photochromism should be used exclusively to describe reversible color changes brought about by light. Such color changes are generally in the visible but are possible in other parts of the spectrum also. Therefore, the term should not be limited to the description of visible color changes. Such phrases as visible photochro­mism, infrared photochromism, and ultraviolet photochromism are vividly descriptive.

To provide a term for an irreversi­ble process, let's first examine the term photochromism in a philological sense. This term is made up of two parts, that is, photo (light) and chrom (color) combined with the ending ism indicating a phenomenon. Literally, it means a phenomenon of light and color but according to its definition by usage it is really a contraction of a word such as "photopalinchromotro-pism." This word contains the addi­tional parts "trop" (change) and "palin" (again or back) and can be translated simply as "a light-induced reversible color change phenomenon" if palin is interpreted as reversible. The word is also philologically com­plete but perhaps too long to use con­veniently and, therefore, the contrac­tion "photochromism" is desirable. The philological composition of "pho-topalinchiOmotiOpism" suggests that a new term can be derived by replace­ment of the part meaning reversible with a new part meaning irreversible. Such an entity is "alio" ("other"). Thus "photallochromotropism" indi­cates literally a light-induced change to another color, implying an irreversi­ble process. Its definition then be­comes "a light-induced irreversible color change phenomenon." The term can be contracted to "photallochro-mism" for practical use and seems to fill the void in terminology.

Other contractions of these terms, which fit well with present usage of terminology, are also possible. For example, "chromotropism," derivable from both the above terms, is a gen­eral term for describing color changes caused by some stimulus. Reversibil­ity, irreversibility, or a chameleon ef­fect as well as the stimulus are stated in context with this general term which is already in use [American Cyanamid Co., Contract DA-19-129-AMC-19(X), Tech. Rept. TS-129, U.S. Army Natick Laboratories, Natick, Mass. 01760].

RICHARD N. MACNAIR Natick, Mass.

This lab demineralizer has a great head

The Barnstead BD-1 "Bantam" demineralizer tells you the quality of water you're getting, as well as when its disposable cartridge should be changed. A built-in, direct reading purity meter makes the difference. No guessing about water purity. No wondering whether you're replacing cartridges too early or late. You know (in parts per million and ohms resistance) at the flick of a switch. Other features of this popular Barnstead BD-1 : Flow rate; 5 to 10 gph — Quick cartridge change, without tools — Comes complete for connection to raw water line, with pedestal, inlet and effluent tubing and valves, electrical cord, plug — Takes only 8" χ 8" χ 28" high bench space, or wall-mounts, See your laboratory supply dealer. Write for Barnstead Catalog 154A.

OCT. 30, 1967 C&EN 7

on its shoulders.

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Barnstead