296 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



that condition. It should be stated, however, that before being salted 

 they should be cleaned very thoroughly, as it is very difficult to remove 

 blood and muscle-tissue from a salted swim. Cleaned sounds, of course, 

 sell much higher, and they are far preferable in every respect to those 

 which have not been cleaned. The most troublesome and time-consum- 

 ing work in the preparation of isinglass is to remove the sound from 

 the backbone, which is still done by hand. This is also the principal 

 reason why more general use has not yet been made of the sounds. This 

 work must be done very slowly, and to produce large amounts of isin- 

 glass would require much labor, which is hard to obtain during the 

 fishing season. If it was possible to use for this work some sort of ma- 

 chine which would meet all the requirements, the manufacture of isin- 

 glass would receive a new impetus. 



Good isinglass should be of a bright (or at least a light yellow) color, 

 thin and transparent, and without any odor or taste, which will invari- 

 ably indicate the presence of impurities. When dissolved in boiling 

 water (in cold water it does not dissolve, but merely turns to a clear 

 jelly) there should remain but a very small insoluble residue, and the 

 jelly which is formed should be clear and colorless. 



A great portion of the isinglass which is at present brought into the 

 market comes from North America. Like the Norwegian fish-glue, it is 

 prepared from the air-bladders of cod,. and does not easily dissolve in 

 water, and a greater quantity remains undissolved than in the Russian 

 isinglass. The method of preparing it is like the one described above, 

 only with this difference, that immediately after having been cleaned, 

 while still in a moist condition, it is pressed between iron rollers, after 

 which it is spread out and dried in the sun. America has of late years 

 made rapid progress in the manufacture of isinglass from fish refuse. 

 The raw material consists to some extent of fish-heads, and especially of 

 fish-skins — the waste products of " boneless fish." The skins are soaked 

 and washed in order to remove salt and all impurities and to prepare 

 them for the following bleaching process, when the isinglass is obtained 

 by boiling them in water, and by clearing the liquid glue and concen- 

 trating it in vacuum-pans. Entirely pure liquid fish-glue is colorless, 

 and, like the pure isinglass, has neither odor nor taste. 



The light and most strongly concentrated fish-glue is used in the 

 manufacture of pianos and various kinds of wooden ware ; a light and 

 less concentrated grade is used in the manufacture of paper ; and a 

 dark and highly concentrated grade is used in the manufacture of hats 

 and shoes. 



Sweden occupies a prominent place among the countries producing 

 isinglass. Manufacturers in Lysekil have sent us excellent specimens 

 of dried isinglass in thick but clear tablets, having a slight yellowish 

 tinge, and gelatine in thin tablets, clear as water. We have been in- 

 formed that these articles have been specially prepared from sounds 

 that had first been subjected to a bleaching process, after which they 



