CHEMISTRY OF A HEN'S EGG. 19 



holes, too small to be discerned with the naked eye, 

 but which, with the aid of a microscope, are dis- 

 tinctly revealed. Under the microscope, the shell 

 appears like a sieve, or it more closely resembles 

 the white perforated paper sold by stationers. 

 Through these holes there is constant evaporation 

 going on, so that an egg, from the day that it is 

 dropped by the hen to the moment when it is con- 

 sumed, is losing weight, and diminishing in volume. 

 This process goes on much more rapidly in hot 

 weather than in cold, and consequently perfect 

 eggs are not so readily procured in summer as in 

 winter. If by any means we stop this evaporative 

 process, the egg remains sound and good for a great 

 length of time. Covering the shell with an imper- 

 vious varnish, or with mutton suet, or lard, aids 

 greatly in their preservation. The substance used 

 to stop transpiration must not be soluble in watery 

 fluids, or liable to be readily removed. By chem- 

 ical agencies, that is, by actually filling up the little 

 holes in the shell by lime placed in contact in solu- 

 tion (the solution holding the proper chemical sub- 

 stances to form an impervious coating of carbonate 

 of lime over the entire surface), we have pre- 

 served eggs for months and even years in a sweet 

 condition. Not long ago, eggs broken in our labo- 

 ratory were found to be quite fresh, which, accord- 

 ing to the memorandum made upon the vessel, were 

 placed in the solution in May, 1867. 



