180 Impioved ^I ill for grinding Indigo, &c. 



colour ; but the bladder, bciug; uninjured, may be used re- 

 peatedlv for fresh quantities ot" colour. 



N. B. The barrel of a qtiill may be tied, in place of the 

 stick, into the neck of tb.e bladder, with its closed end out- 

 wards, which will keep the colour secure in travelling, ana 

 when used, the end of the quill being cut off, it may after- 

 xvards be closed bv a stick. 



XXX. Improved Mill J'or gniiding Indigo, or ether dry 

 Colours*, 



JTlate IV. fill, 2. L represents a mortar made of marble 

 or hard stone : one made in the connnon way will answer. 



M, a niuller or grinder, nearly in the form of a pear, iti 

 the upper part of which an iron axis is firmly fixed, which 

 axis, at the pails NN, turns in grooves or slits, cut in two 

 pieces of oak projecting horizontally from a wall, and when 

 the axis is at work, are secured in the grooves by iron pins, 

 00. 



P, the handle, which forms a part of the axis, and by 

 Tvhich the grinder is worked. 



O, the wall in which the oak pieces NN are fixed. 



K, a weight, which mav occasionally he added, if more 

 power is^ wanled. 



Fig. 3. shows the muHer or grinder, with its axis sepa- 

 rate from the other machineiv : its bottom' should be made 

 U) fit the mortar. 



S is a grof>ve cut througli tlie stone. 



On grinding indigo, or such substance, in a dry state, iii 

 this mill, the niuUcr being placed iu the miMtar, and se- 

 cured iit the oak pieces by the pins, the indigo to be ground 

 is thrown above the muller into the mortar ; on turning the 

 handle of the axis, the indigo in lumps falls into the groove 

 eut through the nudler, aiid is from thence drawn under 

 the action of the muller, and propelled to its oiUer edge 

 within the mortar, from whence the coarser particles again 

 fall into- the groove of the m..ulkr, and are agaiii ground 

 under it; which operation is- contimTed till the whole of it 

 is ground to an impalpabla powder: the muller is then easily 

 removed, and the colour taken out. 



A wood cover, in two halves, with a hole for the axis, 

 is usually placed upon tlw mortar, during the operation, to 

 prevent any loss to the colour, or bad ttffect to th-c operator. 



* From Transit f.oKs (/" //x .% icty of :ht;, 5cc. for j'^o.t. 



XXXI. A 



