1835.] Accidental and Complementary Colours. 



'23 



should be added to the solution previous to the observation, 

 as the archil of commerce sometimes contains an extraneous 

 acid, which imparts a reddish tinge to the dye. 



9. Water slightly impregnated with carbonate of lime, 

 on mercury, yielded a very faint accidental black. 



10. Very dilute black gallate of iron yielded a faint acci- 

 dental reflection of white. 



11. The result of these experiments may be thus 

 arranged : — 



Solutions on Mercury. 



Colours. 



Ocular Spectra. 



slightly red- ) 



by) 



1. Litmus 



dened 



2. Litmus, reddened 



nitric acid . . , . S 



3. Oxalate of ammonia & ^ 



bichromate of potassa 



4. Chromate of potassa. 



Muriate of lime, with 

 excess of acid . 



5. Indigo in sul. acid . 



6. Nitrate of copper . 



7. Sulphate of chromium 



8. Nitrate of Chromium . 



9. Archil 



10. Dilute black gallate i 

 of iron > 



11. Dilute carbonate of i 

 lime 5 



} 



Reddish-purple 



Red 



Orange 



Yellow 



Indigo 



Blue 

 Dark-green 

 Grass-green 



Violet 



Black 

 White 



Light-green. 



Dark-Green. 



Blue. 



Indigo. 



Orange-yellow. 

 Orange-red. 



Red. 



Violet-red. 



Yellowish-green 



Whitish. 



Blackish. 



12. Although these results (with the exception perhaps 

 of 10 and 11), were sufficiently satisfactory; yet, being 

 anxious to introduce into my lectures an easy method of 

 exhibiting these colours, so as to be at once seen and appre- 

 ciated by my pupils, I endeavoured to supersede several 

 objections that were attached to the above mode, and the 

 principal objection was, perhaps, found in the fact, that the 

 mercurial surface soon became tarnished, and the employ- 

 ment of so large quantities of mercury in several glasses, 

 so as to shew all the results at one time, was, at least, in- 

 convenient. I, therefore, proceeded to inquire, whether 

 similar results could not be obtained by means of disks of 

 stained glass. 



13. Of these I procured at first four, each three inches 

 in diameter, a red, a yellow, a blue, and a green. On 



