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A. Preparation of grough from natural saltpetre.

Carefully wash the natural saltpetre, and (as far as possible) remove all impurities. Dissolve it in water over a gentle fire, and boil it until the scum ceases to rise, and it is purified and clarified. Let the operation be repeated again and again, until the solution is clear and bright. Let it then deposit its crystals of the stone which is not a stone,42 and dry them in a warm place.

B. Boiling the solution of grough saltpetre.

Pulverise the crystals of grough saltpetre thus obtained, and immerse them in water. Make a powder of two purifying substances in the proportion of 3:2. Dissolve the crystals over a gentle fire.

F. Use of wood-ash, charcoal, &c.

To the powder add some animal charcoal, and thoroughly incorporate the ingredients (in a vessel). Then pour the hot solution upon it, and your object (of clarifying the mother liquid) will be gained.

C. Removal of the insoluble impurities.

If (by its appearance and taste you judge that) the solution is good, pour it out (into a crystallising vessel, leaving the heavy impurities behind).

G. Crystallisation.

(The mother liquid is now allowed to crystallise.)

H. Stirring the depositing solution.

(While depositing), stir the solution with a pestle. Collect the crystals as best you can, and gradually draw off the mother liquid.

The original is as follows:—

Calcem diligenter purifica, ut fiat terra pura penitus liberata ab aliis elementis. Dissolvatur in aqua cum igne levi, ut decoquatur quatenus separetur pinguedo sua, donec purgatur et dealbetur. Iteretur distillatio donec rectificetur: rectificationis novissima signa sunt candor et crystallina serenitas. Ex hac aqua materia congelatur. Lapis vero Aristotelis, qui non est lapis, ponitur in pyramide in loco calido.

Accipe lapidem et calcina ipsum. In fine parum commisce de aqua dulci; et medicinam laxativam compone de duabus rebus quarum proportio melior est in sesquialtera proportione. Resolve ad ignem et mollius calefac. Mixto ex Phœnice adjunge, et incorpora per fortem motum; cui si liquor calidus adhibeatur, habebis propositum ultimum. Evacuato quod bonum est. Regyra cum pistillo, et congrega materiam ut potes, et aquam separa paulatim.43

TABLE I.

Methods of Refining Saltpetre.

Roger Bacon, cir. 1248	A	B	F	C	G	H	...	...	...	...	...
Hassan er-Rammah, 1275-95	A	F	B	...	...	...	...	...	...	...	...
Liber Ignium, cir. 1300	A	...	...	...	...	...	...	...	...	...	...
Whitehorne, 1560	A	B	F	C	G	I	F´	D	E	D´	G´
Waltham Abbey, 1860.	A	B	C	D	E	F	G	H	I	...	...

A = Preparation of grough from natural saltpetre.

B = Boiling the solution of grough saltpetre.

C = Removal of insoluble impurities.

D = Second boiling of the solution.

E = Filtration.

F = Use of wood-ash, animal charcoal, &c.

G = Crystallisation.

H = Stirring the depositing solution.

I = Washing and drying.

The simple and highly probable conclusion to be drawn from the foregoing facts is, that saltpetre was not discovered until the second quarter of the thirteenth century; but this conclusion is not universally accepted. It is said by some that although saltpetre was unknown to the rest of the world until then, it had been secretly used by the Greeks for five hundred years. This theory will be examined in the following chapter.