Study of Sfnrogyra nitida. 229 



tively narrow band isolated from all the other visible rays 

 of the spectrum, and in which the human eye, aided by 

 the spectroscope, can distinguish only one color. 



Such a band was isolated from each fundamental color of 

 the spectrum, namely, violet, bine, green, yellow, orange 

 and red. To produce these bands the following solutions 

 and mixtures were found to be the most satisfactory. 



A'ioh-t. — Dissolve 128 grains of copper sulphate in 1000 

 cc. of water. Add to this 0.08 grams of Hoffman's violet 

 (blueish) in 40 cc. strong alcohol. A layer one inch in 

 thickness gives a band extending from 449 (ifi. to 417 ////. 



l?l»i<-. — Dissolve 35.5 grams of copper sulphate in 1000 

 cc. of water. 100 cc. of strong ammonia water renders 

 this a clear, deep blue. A layer of one inch gives from 

 476 ftp. to 435 fXfl. 



< ; reen.— Victoria green (3(C 23 H 25 N ; ,C1). 2ZnCl 2 + H 2 0) was 

 taken as the basis for this color. In pine solution, how- 

 ever, it transmitted some of the bine and some red. Ani- 

 line yellow removed the former, and copper sulphate the 

 latter. The quantities used were: 0.32 gram Victoria 

 green in 1000 cc. of water, 0.0454 grams aniline yellow in 

 22.7 cc. alcohol, 16 grams of copper sulphate in 100 cc. of 

 water. The mixture is used in a layer of one inch, yield- 

 ing a band extending from 535 ;m. to 510 u/t. 



Yellow. — This band, being so short, and also the 

 brightest color of the spectrum, proved exceedingly diffi- 

 cult to obtain. Yellow dyes and solutions were very imper- 

 fect, yielding red, orange and green invariably, and fre- 

 quently some bine. 



It has been seen that copper sulphate cuts out the red 

 end of the spectrum, either wholly or in part, according to 

 its concentration. An aniline dye, "mandarin," having 

 the formula C 16 IinNX) 4 SNa and showing a deep orange 

 when in aqueous solution, removes the more refrangible 

 rays. If, then, a ray of white light be allowed to pass 

 through both these liquids we have remaining only the 

 yellow rays, provided the solutions be of the proper con- 



