Intelligetice and Miscellaveotis Articles. 213 



If however two equivalents of sulphuric acid and one equivalent 

 of alcohol be employed, circumstances are altered ; sulphovinic acid 

 is always formed ; and still more, the proportion of sulphovinic acid 

 is always the same, whether the acid be poured into the alcohol or 

 the reverse ; whether metallic vessels be used or not ; and whether 

 they are or are not cooled. The whole of the acid and alcohol do 

 not however combine ; the reaction does not take place on much 

 more than half of the mixture, for not more than 54 of sulphovinic 

 acid can be formed from 100 of sulphuric. This proportion does not 

 change by prolonging the contact, or even by the application of a 

 heat of 212" F. continued for several hours ; the capacity of satura- 

 tion of the acid mixture remains the same. In heating to 212°, the 

 volume is scarcely diminished ; it follows, therefore, that the alcohol 

 which is not changed into sulphovinic acid must be retained by a 

 peculiar affinity. — Ann. de Ch. et de Phys., Fevrier 1847. 



ON A METHOD OF PRODUCING LIGHTS AND SHAI>ES IN EQUAL 

 PERFECTION IN DAGUERREOTYPE PICTURES. BY MM, BEL- 

 FIELD LEFEVRE AND LEON FOUCAULT. 



It was observed soon after M. Daguerre had made known his 

 wonderful discovery, that the iodized plate was not suited for pro- 

 ducing a perfect image of every object, but that if there was a great 

 variety of light and shade, i. e. very light and very dark parts, they 

 would not be simultaneously brought out with correctness : one of 

 these two alternatives must be chosen ; either to stop the process 

 when the light parts of the picture are brought out (in which case 

 the dark parts will not be clearly distinguishable), or to allow the 

 light to act for a longer time, in order to render the dark parts di- 

 stinct , but in this case the light parts will be rendered indistinct, 

 or, as it is called, burnt. 



These evils have fortunately been remedied by the employment of 

 certain substances, which not only allow of the operation being 

 performed with greater rapidity, but also produce sensitive surfaces 

 capable of receiving a much greater variety of tints. These are, 

 however, far from being perfect ; and therefore if any process could 

 be discovered which would bring out the light and dark parts of the 

 picture with equal distinctness, without increasing the sensitiveness 

 of the plates, it would be advisable to have recourse to it in certain 

 cases. If the operator knows how to work well upon these different 

 sensitive surfaces, without confining himself exclusively to the most 

 sensitive, he will be able to produce any effect desired ; for instance, 

 if requisite, he will moderate the intensity of the rays of the sun 

 bearing upon objects of inadequate reflective powers, or heighten 

 the tone of a picture. 



With a view to facilitate the attainment of good results, Mr. Bel- 

 field and myself determined on making known a new mode of pre- 

 paring the sensitive surfaces, the effect of which is to impart to the 

 plates the property above-mentioned, and which assimilates them to 

 the human retina. 



