102 THE VICTORIAN NATURALIST. 



violent poison, which alone makes it unsafe to use in the field ; 

 also, animals left too long in it become very brittle. There 

 is chromic acid and its salts in various strengths, and others. 

 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. Therefore, none are 

 suitable 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 to be 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 for collecting a sufficiently varied assort- 

 ment 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 preserved in alcohol for comparison. 



I have been unable to meet with any complete paper on 

 formalin, but have seen various short extracts in diff"erent 

 scientific magazines, the authors all bearing testimony to its 

 efficacy. 



Before I speak of the properties of formalin, I will endeavour 

 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, C^H^O, 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 C^H^O, which on further oxida- 

 tion is changed to acetic acid, C^H^O^. Formic aldehyde is 

 produced from wood alcohol, and is one of the simplest carbon 

 compounds. One molecule contains CH.O. 



Formalin is water in which 40 per cent, of this aldehyde is 

 contained. All percentages of formalin, or formol, mentioned by 

 any writer, therefore, are not to be considered as percentages of 

 formic aldehyde, but percentages of 40 per cent, of the aqueous 

 solution of that product. (You must note the difference between 

 formalin solution and formalin. The strength of " Formalin Solu- 

 tion " is I oz. of formalin to 80 ozs. of water, so is only i^ per 



