126 
Transactions of the 
pMonthly Microscopical 
L Journal, Sept. 1, 1869. 
Professor Churcli, which when cut at the proper angle gives a 
series of unvarying and equally divided bands throughout the 
spectrum. This mineral substance is even preferable to the nitric 
oxide gas of Brewster, which was proposed for the same purpose 
some time since by Dr. Thudichum ; — claimed lately by the editor 
of the ' Quarterly Journal of Microscopical Science ' as quite a new 
discovery of his own. The spectrometer devised by Dr. Thudichum 
for his laboratory experiments, St. Thomas's, enables him to obtain 
a scale divided into 2000 divisions of the colour spectrum."^ 
At the present moment nothing has been satisfactorily proposed 
for a systematic grouping of the colours ; but it seems to me that 
a preference should be given to the proposal for making the order 
of the bands the basis of our future arrangement. Take the 
normal chlorophyll band, when that has been definitely fixed, as 
group 1 ; then a Tauracine band ; the permanent three bands ^of 
red cinararia ; the six of Berberis ; and those producing general 
absorption might form a distinctive group ; but it would certainly 
be preferable to refer to the absorption bands of chemical salts or 
minerals, as these are more constant. After this has been fairly 
done, may we not hope so to generalize the facts as to apply the 
knowledge obtained to some useful purpose, as that arrived at by 
Professor Koscoe in determining the spectrum of the Bessamer 
process in making steel ? 
In the preparation of the colouring matters of flowers, it is of 
less importance to attempt to get rid of any excess of acid that 
may exist in their petals, than it is when it is wished to extract the 
pure and simple chlorophyll of the leaves of plants, the object 
being that of obtaining the colouring matter in its intensest and 
purest form. To effect this, steeping the petals in water will^not 
serve the purpose, as only very few flowers thus part with more 
than a portion of colour. In some instances it appears to produce 
what may be described as a decomposition ; depriving flowers of their 
chromule, and leaving behind only a colourless solution. Spirrts 
of wine is certainly the most efiicient and widely useful menstruum 
for the purpose of extracting chromule and retaining it unchanged 
for any length of time. I have found methylic, or wood spirits, bisul- 
phide of carbon, chloroform, glycerine and spirit, all useful agents ; 
but although spirits and water are the chief solvents of vegetable 
colours, it frequently happens that they are not equally efficient : 
there is consequently a good deal of variation in the spectrum 
results. 
In the preparation of coloured solutions, I find it better not to 
crush the petals or leaves previous to immersion in the spirit or 
water. Crushing often changes the colour, and, as a rule, it is 
* 'The Chemical Identilioation of Disease/ by Dr. Thudidaum. Tenth 
Report Public Health, p. 192. 1868. 
