December 15, 1922] 



SCIENCE 



689 



the other hand the d and / sequents have as 

 mantisssB multiples of the oun. The last two 

 chapters are given to the monatiomic gases and 

 to the consideration of miseelllaneous questions. 

 This book by Professor Hicks representing 

 extensive researches for data and extended oal- 

 eulations based on 'the material collected and 

 giving the views of one wli» has studied the 

 subject so 'long and ithoi'oughly will prove a 

 welcome addition to a working library. It pre- 

 sents a general and connected view, provides a 

 means of ready refereniee and suggests lines of 

 investigation, It is well indexed and replete 

 with references to original sources. 



Charles E. St. John 



AMERICAN EOSINS 



In a recent report of this committee'^ it was 

 mentioned that a number of satisfacftory sam- 

 ples of eosin had been obtained from American 

 Sources. At the time this early report was 

 published no very definite data were at hand 

 to show how these samples compared with sam- 

 ples of Griibler's eosin. At the present time, 

 however, data have begun to accumulate giving 

 a more satlisfaetory survey of 'the whole situa- 

 tion and it seems time to publish them. 



Eosin is a compound of the phthalein series 

 with a formula essentially as follows : 



-COoK 



There are an almost innumerable number of 

 different eosins on the markeit, differing slightly 

 in chemical composition and 'having quite dif- 

 ferent staining properties and solubilities. 

 They are usually classed in three or four groups 

 denoted in Schultz's Farbstolfbabellon, fifth edi- 

 tion, undeir the numbers 587, 588, 589 and 590. 



Eosin 587 is the stain best known to the 



1 Committee on Standardization of Stains : 

 ' ' Preliminary Report on American Biological 

 Stains," Science, N. S., LVI, 156-160. 



biologist. It is typically the same as the 

 formula given above, namely the potassium 

 salt of tetrabromfluorescein ; but the monobrom 

 and dibrom derivatives are also known, and as 

 they sometimes occur mixed with the teti'abrom 

 compound, the composition of this dye varies 

 somewhat. Its color varies accordingly, be- 

 cause the more bixjmine atoms the bluer the 

 shade. This dye is specified in the trade by 

 such terms as eosin, yellowish eosin, eosin Y, 

 and eosin G, water-soluble eosin, eosin W, eosin 

 Y extra, eosin S extra. 



Eosin 588 and 589 are both known as alcohol- 

 soluble eosin, being only slightly soluble in 

 water, but differ from each other in that 588 

 contains a methyl group in the place of one 

 of the potassium atoms in the above formula 

 while 589 contains an ethyl group in this same 

 position. Number 588 is more correctly called 

 methyl eosin while 589 is called eosin S or 

 primrose. 



Eosin 590 is a compound in which two of the 

 bromine atoms have been replaced by NO2- 

 grioups. This compound, like 587, is readily 

 soluble in water but differs from it i-n its 

 liluish color. It is known as bluish eosin, eosin 

 B or eosin BN. 



It must be undei-stood that with such great 

 variation in the possible composition, every 

 manufacturer puts on the market a product 

 slightly different from that of any other and 

 as these compounds differ in shade each differ- 

 ent product is generally known by its own 

 trade designation. This gives the very con- 

 fusing list of designations applied to eosin, of 

 which those mentioned above are merely the 

 commoner ones. It simplifies matters, how- 

 ever, if it is remembered that the term's eosin, 

 yellowish eosin or water-soluble eosin refer to 

 587, while alcohol-soluble eosin refers to 588 or 

 589 and bluish eosin to 590. 



No attempt was made in this work to get 

 uniformity in the technic tihat was used, each 

 collaborator being asked to use the samples 

 for any purpose and according to any technic 

 with which he was familiar. One of the inves- 

 tigators, in fact, reports five different tesits to 

 which he submitted the samples. As a result, 

 these samples have been tested in a great 



