Ifi4 Miscellaneous Intelligence. 



powder. Hence quick-lime would bo a dangerous desiccator in a pow- 

 der-house. — Annates de Chim. xxiii. 2 J 7. 



9. Purple Tint of Plate Glass affected by Light.— It is well known 

 that certain pieces of plate glass acquire, by degrees, a purple tinge, 

 and ultimately become of a comparatively deep colour. The change 

 is known to be gradual, but yet so rapid as easily to be observed in the 

 course of two or three years. Much of the plate glass which was put 

 a few years back into some of the houses in Bridge Street, Blackfriars, 

 though at first colourless, has now acquired a violet or purple colour. 

 Wishing to ascertain whether the sun's rays had any influence in pro- 

 ducing this change, the following experiment was made : three pieces 

 of glass were selected, which were judged capable of exhibiting this 

 chance ; one of them was of a slight violet tint, the other two purple 

 or pinkish, but the tint scarcely perceptible, except by looking at the 

 edges. They were each broken into two pieces, three of the pieces 

 were then wrapped up in paper and set aside in a dark place, and the 

 corresponding pieces were exposed to air and sunshine. This was 

 done in January last, and the middle of this month, (September,) they 

 were examined. The pieces that were put away from light seemed 

 to have undergone no change ; those that were exposed to the sun- 

 beams had increased in colour considerably ; the two paler ones the 

 most, and that to such a degree, that it would hardly have been sup- 

 posed they had once formed part of the same pieces of glass as those 

 which had been set aside. Thus it appears that the sun's rays can 

 exert chemical powers even on such a compact body and permanent 

 compound as glass. — M. F. 



] 0. On the Uncertainty of Chcmkal Analysis, by INI. Longcham p. — The 

 following is the conclusion of a very interesting memoir on the un- 

 certainty of some results of chemical analysis ; we shall endeavour 

 to return to the memoir at some opportunity. 



" It results from the experiments stated in this work, that the ana- 

 lysis of salts presents an uncertainty of which it is difficult to appreciate, 

 at present, the whole extent ; and that the cause, until now unper- 

 ceived, is, that the sulphates of barytes and lead, and chloride of 

 silver, carry with them, whilst precipitating, some part of the elements 

 in the midst of which they are formed ; and if to this be added the 

 uncertainty presented by the carbonate of lime obtained from the 

 decomposition of calcareous salts, resulting, probably, from the same 

 cause, one will be ready to admit as a general law, that whenever an 

 insoluble salt forms in the midst of a liquid it carries with it a 

 portion of the surrounding substances. This observation, chemically 

 important, probably will be so also to the mineralogist and geologist, 

 inasmuch as it may tell in what circumstance a mineral mass has been 

 formed : for it is probable that the substances which have been found 

 in small quantity only in minerals, have been enveloped at the time of 



