PRACTICAL HINTS 



possible to compare more than a limited portion of one specimen 

 with another under the miscroscope, whereas they can both be 

 thrown upon the screen side by side in their entirety. I have 

 done much work with a small lantern illuminated by the ordinary 

 Welsbach incandescent light and a screen about four feet square. 

 I have in this manner studied the whole of Nordlinger's 1,100 

 sections without injury to them by placing each section between 

 two pieces of glass, which were slid into the lantern in the place 

 of the slide-carrier. 



One detail, which will be found in each description of the 

 separate species, is the colour of the solution produced by boiling 

 the wood in water or alcohol. As is well known, water dissolves 

 gums but not resins, whereas alcohol dissolves resins but not 

 gums. By first boiling a few shavings in water and afterwards 

 boiling them in alcohol, both resins- and gums are extracted. 

 Pigments of various kinds are sometimes more soluble in the 

 one fluid than in the other, and frequently yield useful informa- 

 tion. I make no attempt to enter into the chemical questions 

 that arise from these experiments, but if it be necessary to 

 decide whether a gum be present it can be readily done by 

 noting the white precipitate formed in a solution in water 

 upon the addition of alcohol, and vice versa. 



Tannin may be detected by the application of any iron salt 

 in solution, a test which may prove useful when it is desired 

 to find a wood which will not corrode iron. A solution of 

 caustic potash is a handy reagent, and is indispensable for the 

 testing of the coloured solutions obtained from the wood by 

 extracting with water or alcohol. To those who desire to go 

 more deeply into this fascinating and little-worked branch of the 

 subject, I recommend a little work of great merit by Dr. J. 

 Lauterer (62) as a model of what can and should be done in this way. 

 Items of interest can also frequently be picked up in books upon 

 dyeing, in which the treatment of the various dye-woods, Fustic, 

 Logwood, etc., afford many useful hints. As there are a number 

 of medicinal woods, such as Guaiacum and Quassia, included in 

 the British Pharmacopoeia, that work may be searched with 

 profit. Compared with other branches, this has been well 

 worked, parallel methods to those described in this book being 

 employed in identifying many of our useful drugs and detecting 

 adulterations. Wiesner's fine work (131) should be consulted on 

 these points. 



After noting as much as can be seen with the naked eye a 

 j>ocket lens should be used and will reveal a marvellous amount 

 of detail. In nine cases out of ten it will show all that is needed 

 for the purpose of identifying a wood, for which there is much 

 to be thankful, as a small pocket lens can be a constant 



xxxiv 



