METHODS OF ANALYSIS. 35 
bonate and mix. Add pure sodium peroxid (approximately 0.5 gram) small 
amounts at a time, thoroughly mixing the charge after each addition. Con- 
tinue adding the peroxid until the mixture becomes nearly dry and quite granu- 
lar, requiring usually about 5 grams of peroxid. Vlace the crucible over a 
low alcohol flame (or other flame free from sulphur) and carefully heat, with 
occasional stirring, until the contents are fused. (Should the material ignite 
the determination is worthless.) After fusion remove the crucible, allow to 
cool somewhat, and cover the hardened mass with peroxid to a depth of about 
0.5 cm. Heat gradually and finally with a full flame until complete fusion 
tukes place, rotating the crucible from time to time in order to bring any 
particles adhering to the sides into contact with the oxidizing material. Allow 
to remain over the lamp for ten minutes after fusion is complete. Cool 
somewhat, place the warm crucible and contents in a 600 cc beaker and care- 
fully add about 109 ce of water. After violent action has ceased, wash mate- 
rial out of crucible, make slightly acid with hydrochloric acid, and filter. 
Determine sulphates by precipitating with barium chlorid in the ordinary way. 
SOILS. 
Moisture. 
Dry two or more grams in a tared platinum dish for five hours at the 
temperature of boiling water; cover the dish, cool in a desiccator and weigh. 
Repeat heating, cooling, and weighing at intervals of two hours, until the mate- 
rial ceases to lose weight. Weigh rapidly to avoid absorption of moisture from 
the air. The loss of weight is reported as moisture. 
Sulphur trioxvid.? 
Digest 10 grams of soil on the steam bath for ten hours with 100 ce of 
hydrochloric acid (sp. gr. 1.115), shaking the flask every hour. Carry on this 
digestion in an Erienmeyer flask, provided with greund-glass stopper ending in 
a reflux tube 20 inches or more in length. Remove from the bath and allow 
to settle. Decant the solution into a porcelain dish, wash the insoluble 
residue onto a filter with hot water and continue the washing until free of 
chlorids. Add the washings to the original solution, oxidize with a little 
nitric acid and evaporate to dryness on a water bath. Take up with hot water 
and a few cubic centimeters of hydrochloric acid and again evaporate to 
dryness. Again add water and sufficient hydrochloric acid to effect solution, 
warm and filter, washing until free from chlorids. Again evaporate this 
filtrate to dryness, take up with a little hydrochloric acid and water, and filter 
to a volume of 500 cc. Take 200 cc of the above solution for analysis, evapo- 
rate nearly to dryness to expel the excess of acid, dilute with distilled water, 
heat to boiling, and precipitate by means of barium chlorid. Boil for about 
five minutes, allow to stand in a warm place over night, filter, and determine 
the sulphur trioxid as barium sulphate. 
Arsenic. 
Weigh 1 gram of soil and treat with 25 cc of concentrated arsenic-free 
nitric acid in a small porcelain evaporating dish. Cover with a watch glass 
and digest on the steam bath for four hours, replacing the evaporated acid 
® Official and Provisional Methods of Analysis, U. S. Dept. of Agr., Bureau 
of Chemistry, Bul. 107. 
