1870.] Chemistry. 401 



substances the New York Metropolitan Board of Health found in 

 the air of the opera-houses. Over one hundred specimens of the 

 particles floating in the air, and falling as dust, were collected on 

 plates of glass, and examined under the microscope. The propor- 

 tions of the different ingredients varied, but the same substances 

 were found in all the specimens. The composition of the matter 

 subjected to the microscope was as follows : — The dust of the streets 

 in its finer or coarser particles, according to the height at which it 

 had been collected, with a large proportion of organic elements ; 

 particles of sand, quartz, and feldspar ; of carbon, from coal-dust 

 and lamp-black; fibres of wool and cotton of various tints; epider- 

 mic scales ; granules of starch of wheat ; the tissues of plants, 

 mamly the epidermic tissue, recognized by the stomata or breathing 

 pores ; vegetable ducts and fibres, with spiral markings ; vegetable 

 hairs or down, either single or in tufts of four or eight, and of 

 great variety, and three distinct kinds of pollens. Fungi were 

 abundant, from mere micrococcus granules to filaments of mould. 

 When water was added to a portion of dust from whatever source, 

 and exposed in a test-tube to sunlight or heat for a few hours, 

 vibriones and bacteria made their appearance, and the fungous 

 elements sprouted and multiplied, showing that they maintained 

 their vitality, and proving that the germs of fermentation and 

 putrefaction are very widely diffused. In connection with this 

 subject, it is right to mention here that Mr. Samuelson performed 

 a similar series of experiments six years ago, on dust from all parts 

 of the world.* 



All lecturers who have tried to float and then ignite an explosive 

 balloon will be glad to know the following easy means of effecting 

 this difficult but striking experiment devised by Mr. Patterson. At 

 first the author tried the india-rubber balloons of the toy-shops. 

 From various causes they had failed ; but the chief difficulty was 

 doubtless the tension which made it difficult to secure the gases. 

 Recently the author's attention has been directed to the collodion 

 balloons, obtainable from the philosophical instrument makers, 

 believing that they would suit well, both on account of their light- 

 ness, and on account of the fact that they would wholly disappear 

 on ignition. After a number of trials he has found them to succeed 

 admirably. The method adopted is as follows : — 



A fuse of filter-paper, about 1 inch long and ^ inch broad, is 

 gummed to the side of the balloon near the mouth, and allowed to 

 dry. The latter is then filled with a mixture of 2J volumes of 

 hydrogen gas and 1 volume of oxygen, the mixture being prepared 

 in a separate vessel. The mouth of the balloon is at once tied with 

 a piece of thread to increase the force of the explosion. When the 

 balloon is ready to ascend, a drop of the so-called " Greek fire " 



* See ' Quarterly Journal of Science,' July, 1864. 



