CusACK — On the Melting Points of Minerals. 403 



adhering to it. By cutting a number (say ten) of ribbons at the same 

 time, so as to have them all the same length, and being very careful to 

 have the ends cut away to exactly the same extent, the necessity of 

 plotting a new curve for each ribbon is done away with. After many 

 trials I found that ribbons carefully cut and adjusted properly in the 

 forceps, so that the head of the screw read the same for each ribbon 

 permitted of such being used to the one curve. 



The amount the ribbons are cut away at the ends is very impor- 

 tant, and great care should be used in seeing that they are cut away 

 an equal amount if a common curve is to be used for a number of 

 ribbons. The best method is to cut each separately on a steel with 

 a very sharp knife, but they may also be marked with a needle point 

 and afterwards cut with a scissors. 



When one requires to determine the melting point of a mineral the 

 first step necessary is to reduce that mineral to the finest powder ; for 

 this purpose a diamond mortar and two agate mortars are indispensable. 

 It has been found most convenient to prepare say ten specimens at a 

 time, and keep the specimens when powdered in little well-corked 

 bottles, as, if the powder gets damp, it is harder to put it on the 

 ribbon so nicely as when quite dry. I have always found the best 

 method of placing the powdered mineral on the ribbon is to use a 

 moderately fine needle. By putting the point of the needle into the 

 powder and then placing the point gently on the ribbon, some of the 

 mineral is found to have remained on the latter. If too much remains 

 the superfluous portion may be removed with a clean camel's-hair 

 brush. The smaller the portion under observation is the easier it is 

 to determine its melting point ; especially in the case of minerals that 

 have a tendency to pass through a period of viscosity previous tO' 

 melting. The specimen should always be placed on the ribbon when 

 cold, and the micrometer should be read every day before starting 

 work, also when work is finished. I never found the ribbon to 

 permanently expand more than the 10,000th of an inch when care 

 was taken not to overheat it. The ribbon should always be allowed 

 to cool to its normal temperature before reading, as otherwise it 

 would not have regained its original position. 



The minerals dealt with in this paper are those of very common 

 occurrence, along with such specimens of rarer minerals as could be 

 obtained in their crystalline state, in as pure a condition as possible, 

 to make up a group. 



Considerable difficulty arises, dealing with the subject of the 

 melting points of natural minerals, in obtaining authentic specimens. 



