490 



DYES AKE COLORTJfG- STUFFS, 



three diiFerent substances in as many varieties of the plant ; all of these bodies 

 differing more or less from each other in composition and properties (at least, 

 if we a,re to assume, as correct, the descriptions given of them by their re-* 

 spective discoverers"). 



" I have already hinted that there is no ratio between the external and in- 

 ternal color or structure of a lichen, and the kind or amount of coloring matter 

 it will be found to yield. It is exceedingly natural to suppose that such a ratio 

 should exist ; but, proceeding for some time on this supposition, I was fre- 

 quently disappointed in my results— the most showy and brilliantly colored 

 lichens often furnishing the dullest and most worthless colors. For instance, 

 the bright yellow thallus of Parmelia parietina^ and the beautiful scarlet apo- 

 thecia of Scyphophorm cocciferm^ instead of producing a rich yellow in the 

 one case, and a deep crimson in the other, yielded, respectively, only dirty 

 greenish-yellow and brownish colors. As a general rule I should almost be 

 inclined to say that the finer the color of the thallus of any given lichen, the 

 more is that lichen to be suspected of poverty in valuable coloring matters ; 

 and that, on the other hand, the palest pulverulent or crustaceous species, 

 especially such as are sasicolous, may be expected to yield the most beautiful and 

 valuable pigments [e.g. the Hocellas and Lecanoras). In such circumstances it 

 is necessary to have some test, of easy applicability, of the kind and amount 

 of colorific properties of any lichen, and this fortunately is readily attainable." 



The fourth section of the paper was devoted to the consideration of the 

 various tests of colorific power, which have been recommended by different 

 authors. " Of these, the greater number proceed on the j)rinciple of develop - 

 ing the coloring matter by some alkali, in conjunction with the decomposing 

 action of atmospheric oxygen and water ; others are founded on the re-action 

 between colorific principles of certain of the dye lichens and somo of our 

 ordinarj^ chemical re-agents." The author noticed in particular— 



1. Helot's test, \ 



2. WBstring's tests, \ qualitative. 



3. Stenhouse's test, ) 



4. ,, quantitative. 



Helot's test consists in digesting the dried and powdered lichen or a few 

 hours, at a temperature of 130 degs., in a weak solution of ammonia, sufiiciently 

 strong, however, to be tolerably pungent. One that is fit for the dyer will yield 

 a rich violet red liquor. 



Dr. Westring recommended simply macerating three or four drachms of the 

 lichen in cool spring water, assisting, perhaps, the solvent action of the water 

 by minute quantities of common salt, nitre, quicklime, sulphate of copper or 

 iron, or similar re-agents. If these means failed, after a sufficient length of 

 time had been allowed for the development of color, he digested a fresh portion 

 of the pulverised lichen in water, containing small quantities of sal-ammoniac 

 and quicklime [in the proportion of 25 parts of Water, 1-lOth lime, and l-20th 

 sal-ammoniac for every part of lichen], for a period varying from eight to 

 fourteen days, and by this process, he says, he never failed to develop all the 

 color which the plant was capable of yielding. 



Dr. Stenhouse, of London, one of our latest and best authorities on the 

 chemistry of the lichens, adds to an alcoholic infusion of the lichen, a solution 

 of common bleaching powder (chloride of lime), whereby, if it contain certain 

 colorific principles capable of developing, under the joint action of air, water, 

 and ammonia, red coloring matters, a fugitive but distinct blood -red color will 

 be exhibited. The amount of this colorific matter may be estimated quanti- 

 tatively by noting the quantity of the chloride of lime solution required to 

 destroy this blood-red color in different cases : or the same result may be ob- 

 tained by macerating for a short period in milk of lime — filtering — precipitating 

 the filtered liquor by acetic or muriatic acid — collecting this precipitate on a 

 weighed filter — drying at ordinary temperatures and again weighing. 



The author entered into a full analysis of these tests and processes — 

 pointing out their respective advantages and disadvantages — and shouung their 

 practical value and applicatons. He stated that he had made use of these, and 

 various other tests, in upwards of 300 experiments, and the one which he em- 



