178 
SUMMARY OF CURRENT RESEARCHES. 
scopically owing to the presence of the siliceous envelopes of the algae 
having resisted destruction. The mass to be examined should be treated 
with dilute sulphuric acid and a few crystals of permanganate of potash. 
In this way a thin fluid is formed which is easily sedimented, the sili- 
ceous envelopes of the algae being found in the deposit. 
Disinfection of Books.* — Dr. von Schab records some experiments 
made for the purpose of testing the value of Pict.et y s gas-mixture and 
formaldehyd for disinfecting books from lending libraries. Pictet r s 
mixture consists of equal volumes of sulphurous acid and carbonic acid 
gases. The test objects used were Bacillus pyocyaneus, B. anthracis , 
Staphylococcus pyogenes aureus, and tubercular sputum. 
Neither disinfectant gave satisfactory results. 
Demonstration of Small Quantities of Formaldehyd.f — According 
to Herr L. Keutmann, a solution of hydrochlorate of morphia in strong 
sulphuric acid is very convenient for showing the presence of formal- 
dehyd. One decigram of morphia hydrochlorate is dissolved in 1 cem. of 
strong sulphuric acid. This solution will detect the presence of 1 part 
of formaldehyd in 5000 or 6000 parts. The solution to be tested is 
poured upon (but not mixed with) the morphia solution, and within a 
few minutes assumes a red-violet hue. 
* Centralbl. f. Bakteriol. u. Farasitenk., xxi. (1897) pp. 141-6. 
f Zeitschr. f. ang. Mikr., ii. (1896) p. 267. 
