THE WOMBAT. 87 



These all affect the natural colours to a very great extent, 

 and it is also important that specimens only remain in them 

 for varying periods of duration before being passed into alcohol, 

 which alone allows of extended times of immersion. There- 

 fore, none are suited for a general preservative to take with 

 us in the field, especially if we are on a few days' outing. 

 Alcohol, so far as I know, has been the only preservative used 

 for general work, but I venture to think formalin will be found 

 much better. Do not, however, let me appear as an authority, 

 for my practical experience of it only dates back some eight 

 months, and I have not had opportunities of collecting a 

 sufficiently varied assortment of material. I have, however, 

 brought for your inspection and criticism enough for you to 

 form an impression from. They comprise some 44 examples, 

 all of which have been preserved for at least a month, and 

 most of them longer. They are contained in different strengths 

 and admixtures, and, in some cases, similar structure is pre- 

 served in alcohol for comparison. 



I have been unable to meet with any complete paper on 

 formalin, but have seen various short extracts in different 

 scientific magazines, the authors all bearing testimony to its 

 efficacy. 



Before I speak of the properties of formalin, I will en- 

 deavour to explain its chemistry— presuming you know nothing 

 about it — and those who have had more experience of it than 

 I have will, I trust, bear with me until the close of my remarks. 



Formalin is not a chemical compound, but is the name of 

 a saturated watery solution of the gas formic aldehyde 

 Aldehydes are a series of compounds formed by partial oxidation 

 of the various alcohols, each alcohol forming a particular 

 aldehyde, which on further oxidation is changed into its acid 

 — for instance, ethyl alcohol, or spirits of wine (C2H6O), by 

 oxidation has the chemical affinity holding its atoms together 

 broken, and two atoms of hydrogen are displaced, and a 

 molecule of aldehyde is formed, having the composition C2H4O, 

 which on further oxidation is changed to acetic acid, C2H4O2. 

 Formic aldehyde is produced from wood alcohol, and is one 

 of the simplest carbon compounds. One molecule contains 

 CH2O. 



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