925, 1018, and 1037, with 21.37 to 38.57 per cent phosphoric acid, 
might have a value for making acid phosphate if they were sufficiently 
low in iron and alumina and if they existed in sufficient quantity to 
render their marketing practicahle. 
The values assigned the fertilizing elements were based on usual 
prices prevailing in the eastern part of the United States. They should 
be slightly augmented for Porto Rico, since freight charges raise the 
price of fertilizers in Porto Pico. Transportation to certain interior 
districts of Porto Rico enhances the cost of standard fertilizers still 
further in those districts. On the other hand, it should be borne in 
mind that the valuations given in Tables III and IV are for a dry* ton 
of material. The material as procured from the cave will contain 
considerable moisture, and the value must be reduced according to 
the amount ol moisture. 
In deciding the monetary value of guanos relative xo standard fer- 
tilizers, it should also be borne in mind that the standard commercial 
fertilizers arc uniform products of known efficiency, while the value 
of individual guanos is not so well established. The guanos described 
here which have been subjected to vegetation tests as well as to 
chemical analyses can also be considered as of known efficiency, but 
those which have been merely analyzed are of less certainly estab- 
lished value. For instance, it was shown that the citrate method for 
availability was fairly accurate with 72 per cent of the samples tested 
but very inaccurate with 2S per cent of the samples, the tendency 
being for the citrate method to give too high results. The chances are 
thus about three to one that a chemical analysis will show fairly closely 
the availability of the phosphoric acid. Because of this e^ment of 
doubt a guano high in phosphoric acid not thoroughly tested may be 
worth somewhat less than the valuation given in Tables III and IV. 
All the factors mentioned make it difficult to establish an absolute 
value for the guanos, but it is believed that those given in the tables 
are lair. It will be noted that values of the different guanos varied 
between practically nothing and $47.60 per dry ton, the average for 
the 247 samples tested being $7.1 4. 
GENERAL REMARKS ON BAT GUANOS. 
The analyses and tests reported show the great variation in different 
bat guanos, in respect to their content of the fertilizing elements and 
the availability of these elements. The reasons for the variations are 
given in the first part of this report. Bat guanos, excepting fresh bat 
manure, can not thereiore be regarded as a specific fertilizer in the 
same sense as modern commercial fertilizers, or even the old Peruvian 
guano. 
The fresh bat manure, however, is a fairly definite material in ap- 
pearance, composition, and availability of its phosphoric acid. It is 
