156 



THE AMERICAN MONTHLY 



[August, 



ing the method. So far as we are 

 aware, no person has carried experi- 

 ments in this direction quite so far 

 as he ; and those who have seen his 

 photographs of that very difficult 

 subject, the Bacillus tuberculosis^ 

 cannot fail to recognize the advan- 

 tages of the method. 



The same principle is now applied 

 quite extensively to the copying of 

 paintings, in order to represent the 

 colors in their proper relative strength 

 in the photographs. The so-called 

 ortho-chromatic or iso-chromatic sen- 

 sitive plates, now to be obtained from 

 dealei's in photographic goods, are 

 intended to accomplish the same 

 purpose, but they also require the use 

 of colored screens, to prevent the 

 undue action of the more refrangible 

 rays. Such plates may be found 

 useful in photo-micrography, but it 

 is well to consider that they differ 

 from other plates mainly in their 

 greater sensitiveness to the less 

 refrangible ra3's, while they are 

 scarcely less sensitive to the blue 

 which still preponderates. For this 

 reason, in order to obtain strictly 

 uniform results for all colors, colored 

 screens must be used, particularly 

 when working with sunlight. The 

 great advantage of such plates rests 

 in the fact that they are sensitive to the 

 red and less refrangible rays which 

 do not or only slightlv affect the 

 ordinary plates. 



In this connection we may add 

 the results of an observation quite 

 recently made v^^hich clearly shows 

 the great difference in emulsions of 

 different makers. In developing 

 some negatives on Eastman's paper 

 it was found that they rapidly fogged, 

 and it was at fir.st thought the plates 

 were not good. But the fogging took 

 place in such a way that it was soon 

 suspected to be due to the light in 

 the dark room. On shutting ,off' a 

 great part of the ruby light the nega- 

 tives developed clear. The same 

 light, without screening in any way, 

 has been used for months with the 

 most rapid glass plates in the market. 



svich as Cramer, Stanley, Inglis, and 

 Seed plates, and not a trace of fog 

 could be seen on them. This may 

 explain why some persons assert that 

 they cannot use paper plates. The 

 ruby light should be very carefully 

 tested. 



Detection OF Fat in Butter. — 

 A few more words on this subject ex- 

 tracted from a private letter of Mr. 

 C. M. Vorce, which we take the 

 liberty of printing, will not be amiss 

 at this time, since they indicate very 

 well just what the writer considers to 

 be the character of Dr. Taylor's im- 

 provements upon other processes. 

 Mr. Vorce writes : — 



' In the butter matter I think Dr. 

 Taylor's method of inffuencing the 

 crystallization by removing part of 

 the olein by draining the melted fat 

 is a new modification of the old pro- 

 cesses. Hassall summarizes all that 

 had been done in Taylor's line before 

 Hassall's last edition, viz., to melt 

 the fat and allow it to cool — some- 

 times with repeated melting and cool- 

 ing. But the process appears to have 

 always been done in impervious ves- 

 sels, at all events no mention is made 

 of cooling the fat in a porous or per- 

 vious vessel, nor of any method of 

 removing any part of the least readily 

 crystallizable elements. The result 

 was that, as all fats contained the ele- 

 ments olein and stearin, the crystalli- 

 zation was more or less similar, and 

 the melting point being in each case 

 different, time enough was always al- 

 lowed to enable a thorough cooling. 

 Hence the fat would come back to 

 about the same state it was in at first, 

 and it is no wonder they could tell 

 little or nothing about it. I long ago 

 discovered that by dissolving butter 

 and other fats in ether or carbon 

 disulphide, and allowing crystals to 

 form by partial evaporation, different 

 crystals would form from each fat. 

 This I presume was not new. I do 

 not know whether it was or not, but 

 at all events it did not touch Taylor's 



