FARMERS' REGISTER— ANALYSIS OF GYPSUM. 



S3 



PLAIN DIRECTIONS Foil ANALYZING GYPSUfll. 



For the Farmers' Register. 



It is not quite so ca.sy to analyze gypsum, and 

 ascerlain tlie precise proportions of any Ibreign 

 admixlures, as may be done with marl. Still it is 

 not dill:.',ult, nor very troublesome, to go through 

 such a process as will enable any larmer to avoid 

 being deceived by any adulteration of gypsum of- 

 fered ibr sale. In the pulverized state, as pre- 

 pared for manure, it is impossible to detect the 

 grossest and most injurions fraud, by merely the 

 appearance or taste, or by handling the article. If 

 chalk, and very white clay, (such as fonns some 

 of the subsoils in Nelson county) were used to 

 make half the weight of what is sold for g3'psum, 

 it would scarcely be detected — and many iLn-mers 

 might be cheated with a mixture containing not 

 even the smallest proportion of gypsum. I know 

 not whether such trauds are attempted — (and the 

 character of the mills in Vii'ginia is enough to 

 guarantee the purhy of their ground gypsum — ) 

 out if attemjoted, there is nothing whatever to 

 prevent their succeeding, unless chemical tests are 

 employed for detection. The inspectors of gyp- 

 sum appointed by law, who, it is to be presumed, 

 judge altogether by the appearance, and other 

 "sensible qualities, are no saleguard against decep- 

 tion: and this particular branch of the inspection 

 system, is even more useless, more deceptions, 

 and operating more as a cheat upon the communi- 

 ty, than the inspection of any other commodity 

 whatever. I mean not to reflect on any individu- 

 als by these remarks: the fault is in the system, 

 and not in the persons appointed to carry it into 

 operation But this is wandering from my sub- 

 ject. 



Not being entitled to be considered either an 

 operative or scientific chemist, I do not know 

 whether a more correct and convenient method 

 of analysis may not be practiced than mine; and 

 there may exist in this, causes to produce inaccu- 

 rate results, which my ignorance, lias prevented 

 my discovering. If so, I hope some other person 

 will point out my mistakes. 



G)'psum (sulphate of lime) is composed of cer- 

 tain proportions of sulphuric acid, lime, and water, 

 chemically combined. Some small admixtures of 

 metal, &c. which always accompany the gyjisum 

 of commerce, are too inconsiderable to affect the 

 value materially, or to be ascertained by the pro- 

 cess which will now be directed. Considerable 

 admixtures of substances which could deceive the 

 purchaser of ground g\-psum, must be of clay, or 

 chalk. If sand, or silicious earth was contained 

 in g}q:)sum, it would be evident enough to the 

 teeth of the examiner. 



1. Let a certain quantity, say 100 gi'ains, of 

 gypsum of commerce be pounded finely, when 

 quite diy, and then tried with muriatic acid, in the 

 manner directed page 609, No. 10, of the Farmers' 

 Register, for analyzing marl. Pure gypsum will 

 not show any effervescence, or other effect, from 

 the application of muriatic acid. But if there is 

 any efferv^escence, it proceeds from the presence 

 of chalk, or carbonate nf liriie, in some other form: 

 and the proportion of this substance must be as- 

 certained by the directions given in the paper just 

 refeiTed to. 



2. Then put into a glass another portion of the 

 same article, say 25 grains, (finely pounded and 



Vol. II.— 5 



sifted through muslin, belbre being weighed,) and 

 pour to it a saturated (or very strong) solution of 

 carbonate cf potash (which the apothecaries sell un- 

 der the name oi'the super carbonate.yrhe two com- 

 pounds thus placed in contact, sulphate of lime and 

 'carbonate of potash, Avill decompose each other, 

 and exchange princij les in this manner: the 

 suli)huric acid of the liist, will leave the lime and 

 combine with the potash of the solution — and the 

 lime will combine vrith tlic carbonic acid let loose 

 Irom the j.otash: or rather with a ];art of it — lor 

 the lime cannot hold as much carbonic acid as the 

 potash lets go, and the sur])lus escapes into the 

 air with' slow but continued eliervescence, which 

 lasts as long as the process is going on. 



3. When the effervescence ceases, (which may 

 take sorne hours, and plenty of time should be al- 

 lowed,) the chemical qualities of the mixture are 

 totally changed. There no longer remains a par- 

 ticle of sulphate of lime, nor of carbonate ol' pot- 

 ash, (except the excess of the latter, wiiich haAing 

 nothing to operate on, remains unchanged.) In- 

 stead of these, there has been formed the sulphate 

 of potash, and the carbonate of lime — the tojiner 

 being dissolved in the fluid, and the latter in a so- 

 lid form at the bottom of the glass. The appear- 

 ance of the mixture is not perceptibly changed. 



4. Pour off the clear fluid, and then add diluted 

 muriatic acid slowly to the solid matter, which (if 

 f^e gypsum was pure) Avill dissolve all that is solid 

 (then carbonate of lime) Avith effervescence. If 

 there was either clay or sand with the gypsum, 

 they v\all remain at the bottom, after the action of 

 the acid has ceased (as before described in the 

 analysis of marl,) and may be separated by the 

 filtering paper, and after being washed and dried, 

 their Aveight will shoAV the proportion of such im- 

 purities. . ' 



WhateA^er small metallic proportion may be in 

 gypsum, Aviil be dissolved by the acid, and not 

 shoAv in the result (as it should do,) as a part of 

 the impurities. With this small exception, all the 

 remainder of the matter dissolved may be consi- 

 dered as carbonate of lime, and Avhich had been at 

 first sulphate of lime, or pure gypsum, after de- 

 ducting as much as Avas dissolved in the first step 

 of the process. 



■ Supposing then that 10 grains of the .100 had 

 been dissolved by the muriatic acid, in the first 

 trial — and that 7 per cent, of solid matter remained 

 after the last, the proportions might be stated as 

 fblloAVs: 



100 grains of gypsum of commerce consisted of 

 Carbonate of Ume, - - 10 grain.?. 



Clay and sand, - - - 7 " 



Pure gj'psum, - - - 83 " 



100 



The foregoing proportions AA'ould mark very 

 impure, if not adulterated gypsum — though it is 

 not more impure than some I recently tried Avhich 

 Avas ground at the north. A specimen of the 

 gypsum ground at Haxall's mill in Richmond, 

 contained one per cent, of carbonate of lime only 

 — Avhich very small proportion may perhaps ge- 

 nerally accompany the rock, or it might have been 

 an accidental admixture, caused by lime having 

 been landed on the same Avharf. 



E. R. 



