APPENDIX. 



telescopic adjustment, to enable the division between tin- two 



ofihe quartz to be clearly seen. 



In using this instrument, the end b should be placed opposite the 

 brightest 'part of a lamp Maine, and it is advisable to cover the flame 

 with an earthenware cylinder having an aperture which just admits 

 tin- end ol the Baccharimeter, so as to shut oil' all light except that which 



through the instrument. The x.ero of the vernier having been 

 placed opposite that of the scale, the operator looks into the end , and 

 adjusts the telescope till the dark line in the centre of the field is clearly 

 tle'tiiied. If the two sides of tin- field are of exactly the same tint, he 

 may proceed with the operation, but if they are not, he must adjust 

 them by m- -TCW and key. which are not represented in the 



en^rav'mir. The tube is then to be tilled with the tluid to lie examined, 

 and it- i by a piece of glass and a metal cap, which should 



not be sereued tOO tightly. The tluid must be transparent, and as 

 dole, A fight yellow color does not interfere with the 

 accuracy of the determination, but a red or brown color impairs it 

 seriously. Three tubes, 1. i.'. and \ a decimetre in length, are generally 

 Supplied with each instrument, and the longer the tube used, the more 

 exact is the determination. Dark fluids may be examined in the 

 >horier tubes, but if very dark they should be diluted before examina- 

 tion. The tube is then placed in the space o <>, and the rack r is turned 

 till the two halves of the field present exactly the same tint. By turn- 

 ing the prUni ,/, different colors of the field may be obtained ; a pale 



lor is that in which dill'erences of the two halves can be most 

 readily observed. The distance to which the y.ero of the vernier has 

 been moved from that of the scale to one or other side, indicates the 

 amount of dextro- or hevo-rotation. The compensator is so graduated 

 that each decree of the scale corresponds to one gramme of sugar or 

 albumin in 130 cub. cent, of iluid when a tube one decimetre long is 

 used. When tubes of a diH'erent length are employed, the number of 

 divided by the length of the tube in order to find out 

 the strength of the solution. As sugar and albumin rotate the rays in 

 a dim-rent direction, their amount cannot be determined when both are 

 in a solution, the instrument then indicating merely the dilfer- 

 enee between their rotating power. In such a case the albumin must 

 be relumed and the amount of sugar determined. The ditl'erence 

 between the rotation caused by the sugar alone and the sugar and 

 albumin together, will then of course give the rotation due to albumin. 

 This instrument may also be used for distinguishing between substances, 

 such as albuminous bodies, which nearly resemble each other in their 

 ireneral characters and reactions, hut have different powers of rotation 

 or specific rotation. Tin. *yr///V rotation of a substance is the extent 

 t> which a solution of one gramme in one cubic centimetre, contained 

 in a tube one decimetre long, will rotate a ray of light passing through 



rotation of light to the right, a 4-' is prefixed to the 



number of degrees through which the beam is turned, and a to indi- 

 :aiion to the left. The specific rotation of sugar is -f ^(\ ; that 



of albumin 66. To find out the specific rotation of aoy substance 



with the saccharimcter, the following formula is used (Iloppe- 



: I : 



u<ual symbol for the specific rotation for yellow light, n is 



::ition indicated on the scale. // the weight of 'the substance in 



grammes contained in MM) cub. cent, of the solution, and I the length 



