4 L. H, Borgström. . (LVII 



and at the meltingpoint at once change iiito a clear liqiiid, 

 which is iuvisible as loiig as the testtube is kept in the bath, 

 biit becomes visible as a verv fluid, transparent liquid if the 

 testtube is lifted from the bath and held up to the light. 

 A couple of milligrams in a capillary of less than 1 mm in 

 diameter are in such case sufficient to give as accurate values 

 as only the arrangement för the taking of the temperature 

 allows. The fusion of other minerals for inst. auripigment 

 is accompanied by a change of colour, by which the transition 

 to the fluid state is much more easily detected, than it 

 would otherwise be. Even the fusion of opaque and me- 

 tallic minerals may be visible in the bath, if a fluid product 

 is formed, in which ascending gasbubbles can be detected 

 at 1° to 2° above the meltingpoint. If it is difficult 

 to perceive if the point of fusion is passed or not without 

 taking the capillary from the bath, it may be removed from 

 time to time and studied. The slender capillary and the 

 sample can carry only a very small quantity of heat and 

 they cool very rapidly and allow immediately after they are 

 taken from the bath of an investigation with the magnifying 

 glass or the microscope. Rounded edges on the mineral- 

 particles are usually a sign that the temperature of fusion 

 is near. The nearing of the meltingpoint of several minerals 

 can be proved by a sintering together of the particles in the 

 sample. It is often advantagous to shake the capillary, or 

 to introduce a finewire into it in order to test if sintering has 

 taken place and to find out the degree of the sintering. The 

 fusion is quite evident if the sample consists of one solidified 

 mäss, in which round airholes testify that it has been tho- 

 roughly liquefied. To facilitate the investigation it is some- 

 times appropriate to crush the capillary with a hammer and 

 lay bare the sample. As a repeated test requires only a 

 small quantity of the mineral and takes very little time this 

 operation can be performed without inconvenience. This 

 last modification of the procedure shows great analogy to 

 methods, which have been employed by several investiga- 

 tors to give decisive answers to questions on melting- 

 points. For this purpose they have kept a portion of the 



